Ukraine: 15 bodies found after attack

• NEW: At least 17 dead and six injured after attack on refugee convoy, Ukrainian officials say


• NEW: Fighting near the scene of the convoy attack prevents access for investigators


• Delivery of Russian aid is stalled pending safety guarantees, a Ukrainian official says


• Fighting continues for control of the Luhansk and Donetsk regions

Kiev, Ukraine (CNN) -- At least 17 people were killed and six injured in an attack on a refugee convoy in the eastern Luhansk region, Ukrainian authorities said Tuesday.

Fighting continues around the town of Lutuhyne, near where the convoy was attacked, the website of Ukraine's counterterrorism operation said.

The injured are hospitalized there, but the perimeter of the area is under fire, so no investigators or journalists can reach the scene.

A spokesman for Ukraine's National Security and Defense Council earlier said that the bodies of 15 civilians had been recovered as of Monday night.

Col. Andriy Lysenko told a press briefing in Kiev that Ukrainian forces were being prevented from recovering other casualties by "fighting in the area which is still controlled by the separatists."

The Ukrainian military said Monday that women and children were among those killed in the attack on the caravan of refugees.

Clouds of smoke are seen on the horizon as Ukrainian forces and pro-Russian rebels clash in Yasynuvata, a suburb of Donetsk, Ukraine, on Tuesday, August 19. For months, Ukrainian government forces have been fighting pro-Russian separatists near Ukraine's border with Russia. The fighting has left more than 2,000 people dead since mid-April, according to "conservative" estimates from United Nations officials.

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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The civilians were trying to escape fighting between pro-Russian rebels and the Ukrainian military but were not in an established humanitarian safety corridor when they came under fire, a military representative said.

Lysenko said Tuesday that the convoy was traveling from Luhansk to Lutuhyne when it was attacked.

Militants are now blocking access to the area around the destroyed convoy and are shooting at all vehicles in the area, he said.

Meanwhile, fierce fighting continues for control of the city of Luhansk, a stronghold for pro-Russian rebels.

The Ukrainian military has retaken one district, Lysenko said, and there is street fighting in the city center.

Aid convoy halted

Humanitarian agencies say thousands of people in the Luhansk and neighboring Donetsk regions don't have access to water, electricity and proper medical aid.

Ukrainian officials acknowledged Sunday that a convoy of more than 260 Russian vehicles on the border is, in fact, carrying humanitarian aid.

But Lysenko said the aid had not started to move as of Tuesday morning, since the rebel Donetsk People's Republic has not given the necessary safety guarantees to the International Committee of the Red Cross.

A small group from the ICRC has been sent to Luhansk to evaluate the situation there and assess how to proceed with the cargo delivery, he said.

As of Tuesday, 77 cities and villages in Donetsk region are without electricity.

The convoy initially sparked fears that Russia was trying to use a humanitarian convoy as a cover for sending in more aid and weapons for pro-Russian rebels in eastern Ukraine, which Russia and the rebels denied.

The ongoing fighting -- sparked by a political crisis over whether Ukraine would seek closer ties with Europe or Russia -- has left more than 2,000 people dead and just under 5,000 wounded in eastern Ukraine since mid-April, according to estimates from U.N. officials.

Diplomatic moves

Efforts to find a diplomatic solution to the crisis in eastern Ukraine continue.

Ukrainian President Petro Poroshenko spoke by phone Monday with German Chancellor Angela Merkel, his office said. That conversation followed a meeting in Berlin on Sunday of the foreign ministers of Germany, Ukraine, France and Russia.

"We discussed the question of how we can find ways to reach an urgently needed ceasefire in eastern Ukraine," German Foreign Minister Frank-Walter Steinmeier said. "We discussed the question of how we can improve and optimize controls at the Russian-Ukrainian border."

Russia's Foreign Ministry said "some progress" had been made on issues including ending the hostilities, border control, the delivery of humanitarian aid and creating the conditions for a political settlement.

Poroshenko also spoke Monday and Tuesday with European Commission President Jose Manuel Barroso, when the Ukrainian leader slammed the attack on the refugee convoy and pointed to "continuing provocations of the Russian Federation aimed at escalation of the security situation in the region."

Poroshenko and Russian President Vladimir Putin are due to meet in Belarus next week at a summit also involving EU officials and the leaders of Belarus and Kazakhstan, the Kremlin said. Those two nations are members, with Russia, of the Eurasian Customs Union, a trade bloc.

Ukraine signed a trade agreement with Europe this year in defiance of Moscow's wishes.

READ: Q&A: What's happening in Ukraine?

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Journalist Victoria Butenko reported from Kiev, and CNN's Laura Smith-Spark wrote in London. CNN's Lindsay Isaac and Will Ripley contributed to this report.