Ukraine detains Russian soldiers

• NEW: Ukrainian President Petro Poroshenko says talks could decide future peace of Europe


• Russian President Vladimir Putin says military escalation will not end conflict


• Ukraine's Security Service says 10 Russian soldiers were detained in the Donetsk region


• Russian state media cites a source saying the soldiers crossed the border accidentally

Slovyansk, Ukraine (CNN) -- Ten Russian soldiers were detained in the Donetsk region of eastern Ukraine, that country's Security Service said Tuesday, as tensions simmered over the conflict between Ukrainian forces and pro-Russian rebels.

The Russian soldiers were captured with documents and weapons on them, the Security Service said.

Russia has repeatedly denied claims by Kiev that it has sent troops and weapons over the border into Ukraine, where the Ukrainian military is fighting pro-Russian rebels.

Russia's state-run RIA Novosti news agency cited a source in the Russian Defense Ministry as saying the soldiers had been patrolling the border and "most likely crossed by accident" at an unmarked point.

Ukrainians fight to survive amid siege

Questions return with Russian convoy

Pro-Russian separatists escort captured Ukrainian army soldiers in a central square in Donetsk, Ukraine, on Sunday, August 24. Ukrainian government forces have been battling pro-Russian rebels near Ukraine's eastern border with Russia. The fighting has left more than 2,000 people dead since mid-April, according to estimates from U.N. officials.

People yell as Ukrainian prisoners are paraded through Donetsk in eastern Ukraine on August 24.

A pro-Russian rebel delivers a speech atop a damaged Ukrainian armored personnel carrier in Donetsk on August 24. Ukraine has recently retaken control of much of its eastern territory bordering Russia, but fierce fighting for the rebel-held cities of Donetsk and Luhansk persists.

People look at damaged Ukrainian military equipment in Donetsk on August 24.

The first trucks of a Russian aid convoy roll on the main road to Luhansk in eastern Ukraine on Friday, August 22. The head of Ukraine's security service called the convoy a "direct invasion" under the guise of humanitarian aid since it entered the country without Red Cross monitors.

A pro-Russian rebel holds shrapnel from a rocket after shelling in Donetsk, Ukraine, on August 22.

Residents sit in a makeshift bomb shelter during a shelling in Makiyivka, Ukraine, on Wednesday, August 20.

Dogs play together as a Russian convoy carrying aid supplies stops at a border control point with Ukraine, in the Russian town of Donetsk, in the Rostov-on-Don region on August 20.

Ukrainian forces take their position not far from Luhansk, Ukraine, on August 20. Ukrainian troops made a significant push into rebel-held territory in eastern Ukraine, claiming control over a large part of Luhansk and encircling the largest rebel-held city, Donetsk, in fighting that has left at least 43 dead.

Clouds of smoke are on the horizon as Ukrainian forces and pro-Russian rebels clash in Yasynuvata, a suburb of Donetsk, Ukraine, on Tuesday, August 19.

An Ukrainian helicopter flies near Kramatorsk, Ukraine, on August 19.

Ukrainian soldiers load a missile during fighting with pro-Russian rebels Monday, August 18, near Luhansk, Ukraine.

Boys play at a refugee camp, set up by the Russian Emergencies Ministry, near the Russian-Ukrainian border on August 18.

Ukrainian soldiers carry weapons at a checkpoint near Debaltseve, Ukraine, on Saturday, August 16.

Pro-Russian rebels greet each other as they pass near Krasnodon, Ukraine, on August 16.

A fireman tries to extinguish a fire after shelling in Donetsk on August 16.

Ukrainian border guards patrol near Novoazovsk, Ukraine, on Friday, August 15.

Trucks of a Russian humanitarian convoy are parked in a field outside the town of Kamensk-Shakhtinsky, in the Rostov region of Russia about 20 miles from the Ukraine border, on August 15. Ukrainian officials were preparing to inspect the convoy, which was bound for the conflict-torn east.

A truck driver from the convoy jumps out of a trailer on August 15. The Ukrainian government had expressed fears that the convoy was a large-scale effort to smuggle supplies or troops to pro-Russian rebels.

A tank belonging to pro-Russian rebels moves along a street in Donetsk on August 15.

A Ukrainian soldier walks past a line of self-propelled guns as a column of military vehicles prepares to head to the front line near Illovaisk, Ukraine, on Thursday, August 14.

A Ukrainian soldier prepares a mortar at a position near Illovaisk on August 14.

A man inspects damage at his house after a shelling in Donetsk on August 14.

A convoy of trucks, which Moscow said was carrying relief goods for war-weary civilians, moves from Voronezh, Russia, toward Rostov-on-Don, Russia, on August 14.

Pro-Russian rebels on the outskirts of Donetsk stand at a checkpoint near a bullet-riddled bus on Wednesday, August 13.

A pro-Russian rebel inspects damage after shelling in Donetsk on Thursday, August 7.

Smoke billows from a Ukrainian fighter jet crash near the village of Zhdanivka, Ukraine, on August 7.

Residents of eastern Ukraine cry in a hospital basement being used as a bomb shelter August 7 in Donetsk.

Ordnance from a Ukrainian rocket launcher shoots toward a pro-Russian militant position in the Donetsk region on August 7.

Relatives of Ukrainian military member Kyril Andrienko, who died in combat in eastern Ukraine, gather during his funeral in Lviv, Ukraine, on August 7.

Refugees from southeastern Ukraine wait at a refugee camp in Donetsk on Wednesday, August 6.

A pro-Russian rebel adjusts his weapon in Donetsk on August 6.

Men walk past a bomb crater in Donetsk on August 6.

A man steps out of his car as Ukrainian soldiers inspect the vehicle at a checkpoint in Debaltseve on August 6.

Ukrainian servicemen sit on a bus near Slovyansk, Ukraine, on Tuesday, August 5.

A pro-Russian separatist guards a road as Australian, Malaysian and Dutch investigators prepare to examine the crash site of Malaysia Airlines Flight 17 near the village of Rossipne, Ukraine, on August 5. U.S. and Ukrainian officials allege that a Russian-made missile shot down the plane from rebel-held territory, killing all 298 people on board. Russia and the rebel fighters deny involvement.

Rescue workers carry the body of a woman who was killed during a bomb shelling in Donetsk on August 5.

A boy stands in a hallway of a refugee hostel run by pro-Russian rebels in Donetsk on Monday, August 4.

Ukrainian servicemen from the Donbass volunteer battalion clean their guns Sunday, August 3, in Popasna, Ukraine.

Ukrainian soldiers fire shells toward rebel positions near Pervomaysk, Ukraine, on Saturday, August 2.

Ukrainian troops patrol near the village of Novoselovka on Thursday, July 31.

A woman says goodbye to her mother as she flees her home in Shakhtersk, Ukraine, on Tuesday, July 29. See more photos of the crisis from earlier this year

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Photos: Crisis in Ukraine

The development comes as Ukrainian President Petro Poroshenko and his Russian counterpart, Vladimir Putin, meet for the first time since June.

The two leaders are in Minsk, the capital of Belarus, for talks related to the Eurasian Customs Union, a trade bloc made up of Russia, Belarus and Kazakhstan -- with the crisis in Ukraine expected to dominate.

As the talks started, Poroshenko said "the fate of the world and Europe" could be decided in Minsk. "We must jointly find the only right decision. Peace on the continent depends on it," he said, according to his office.

Senior European Union officials, headed by EU foreign policy chief Catherine Ashton, are also in Minsk for the summit.

"The EU is attending to see if discussions can help create momentum for a new political solution to the crisis in Ukraine," said Ashton's spokeswoman, Maja Kocijancic.

Putin: Military escalation won't solve crisis

Putin was cited by Russian state media as telling fellow leaders that the crisis in Ukraine "cannot be solved through further escalation of the military scenario."

He said Russia was "ready to exchange opinions" on the conflict and urged dialogue to find a peaceful resolution, state news agency ITAR-Tass reported.

Earlier, Poroshenko spoke with Ashton about the situation in his country's east and the detention of the 10 Russian soldiers, his office said.

He urged the world to support Ukraine and its efforts to secure its border with Russia "to prevent cross-border infiltration of weapons, military equipment and mercenaries." This, he said, would swiftly resolve the situation.

The conflict was first sparked last year by a political crisis over whether Ukraine would seek closer ties with Europe or with Russia. The ouster of pro-Moscow President Viktor Yanukovych in February was followed by Russia's annexation of Ukraine's Crimea region in March and a declaration of independence by separatist leaders in the Donetsk and Luhansk regions.

Poroshenko in June signed a landmark EU trade pact, despite opposition from Russia.

On Tuesday, after meeting with Ashton, the President said Ukraine would ratify the Association Agreement with the European Union in September and immediately send the ratification documents to Brussels.

The move "is in no way aimed against anyone," Poroshenko said, according to a statement from his office. "Instead, the agreement will positively affect relations with all our neighbors, especially in the economic sphere. We would like our international partners to accept our decision."

He added that parliamentary elections scheduled for October 26 should not affect the EU agreement. Poroshenko's trip to Belarus comes a day after he dissolved Ukraine's parliament.

However, Putin warned that it would cost Ukraine billions of euros to try to meet EU trade standards and that Russia, Belarus and Kazakhstan would also lose out. Ukrainian imports would no longer be given preferential treatment, he added.

It's not yet been confirmed whether Putin and Poroshenko, who last met briefly during D-Day commemorations in France, will hold bilateral talks while in Minsk.

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'I just want to survive'

Meanwhile, fighting continues for control of Luhansk and Donetsk, both strongholds for the rebel fighters.

Ukraine's National Defense and Security Council said Tuesday that militants and the Russian military have become more active in the east and south of Donetsk, as well as along the border, with 29 clashes in the past day.

Rebel fighters continue to cross the border, backed up by the Russian military firing over the border, NDSC spokesman Col. Andriy Lysenko told reporters at a briefing.

Four Ukrainian border guards died and three were injured when two Russian Mi-24 helicopters fired on them, he said.

Russia denies direct or indirect involvement in the fighting and says Ukraine's assault against the rebels is precipitating a humanitarian crisis.

The besieged city of Luhansk has been without water and power for over three weeks, city officials said Sunday. Shelling has caused major damage there and in surrounding villages over past weeks.

Members of the Mahounin family told CNN how they fled their town two days earlier. Intense shelling meant they'd had to spend 24 hours a day in an underground bomb shelter with more than 100 others.

"I don't care what they're fighting for, I just want to survive -- I want my son to survive," said Lilia Mahounin.

Aid convoy

Lavrov told reporters that Russia hopes to send a second humanitarian aid convoy to Ukraine this week to help civilians caught up in the conflict.

Last Friday, a convoy of 227 Russian trucks crossed that country's border into eastern Ukraine without Kiev's authorization, a move condemned by international powers as a violation of Ukraine's sovereignty. Officials in Kiev referred to it as an invasion.

The trucks left a day later, having successfully delivered supplies to Luhansk, Russian authorities said. Ukrainian authorities said they suspected the delivery had been used to bolster rebel forces.

U.N. officials estimate that more than 2,000 people have died and nearly 5,000 have been wounded in eastern Ukraine since mid-April.

German Chancellor Angela Merkel, on a weekend visit to Kiev, promised Ukraine loans worth 500 million euros to help rebuild shattered infrastructure and homes.

Rebels parade captured Ukrainian soldiers in streets of Donetsk

Donetsk: Photos of a besieged city draining of life

CNN's Diana Magnay reported from Slovyansk, journalist Victoria Butenko reported from Kiev, and CNN's Laura Smith-Spark wrote and reported in London. CNN's Alla Eshchenko and Matthew Chance in Moscow contributed to this report.