Putin issues retaliatory ban on imports

• NEW: Sanctions are "putting enormous pressure" on Russia's economy, Obama says


• President Putin bans imports from countries that imposed sanctions on Russia


• Details of banned products still to be worked out


• Russia gets 16% of all its imports from the European Union

Moscow (CNN) -- Russian President Vladimir Putin has named a new target as global sparring over Ukraine grows: food.

In a decree signed Wednesday, Putin banned food and agricultural imports from countries that have imposed sanctions against his country.

The retaliatory move comes more than a week after the United States and European Union increased economic sanctions on Moscow for supporting pro-Russian separatists fighting Ukraine government forces in the eastern regions of Donetsk and Luhansk, along the border with Russia.

A list of specific products and food bans is still being worked out by the Russian government, according to the decree, which describes the order as a special economic measure "aimed at ensuring the security of the Russian Federation."

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Russia is Europe's largest importer in value of animals, meat, dairy products, fruits and vegetables, according to the European Union.

And goods from the EU represent 16% of all Russian imports, EU numbers show.

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Putin said measures would be taken to prevent a jump in food prices in Russia.

A senior U.S. administration official told CNN a ban in imports will only deepen Russia's international isolation and work against the country's own economic interest.

"Russia's Central Bank yesterday pointed out that bans on imported food will push up Russia's already high inflation rate, eroding the purchasing power of Russian citizens," the official said.

The United States insists that sanctions against Russian businesses and individuals are having and effect and already weakened Russia's economy.

"Sanctions are working as intended in putting enormous pressure and strain on the Russian economy. ... The economy has ground to halt," U.S. President Barack Obama told reporters on Wednesday.

If Putin doesn't push to resolve problems in eastern Ukraine through diplomacy and peaceful means, Obama said, "he's going to be hurting his economy and his own people over the long term."

But so far, Obama said, violence in Ukraine hasn't stopped even as sanctions against Russia have increased.

"The issue is not resolved yet," he said. 'You still have fighting in eastern Ukraine. Civilians are dying."

Russia has denied allegations that it's supporting separatists in Ukraine and maintains that it wants to see a diplomatic solution to the crisis. But U.S. and Ukrainian officials have accused Russia of saying one thing while doing another -- building up troops along the border and continuing to send support to pro-Russian separatists.

Several countries imposed sanctions on Moscow after Russia annexed Crimea in March, which escalated the Ukraine conflict following the ouster of pro-Moscow President Viktor Yanukovych a month earlier.

Since then, tensions have simmered and flared in Ukraine, with frequent battles between Ukraine government forces and pro-Russia separatists in the eastern part of the country.

A new buildup of Russian troops along the Ukraine border raised concerns Tuesday that Moscow might be contemplating another intervention like the annexation of Crimea.

According to a NATO official, Russia now has about 20,000 troops stationed "in an area along the entire border with eastern Ukraine." The buildup nearly doubled the troop deployment in the last week by adding 8,000 more forces to 12,000 already there, the official said.

In addition, Russia's Defense Ministry is staging a week of military exercises involving air troops and anti-missile defense forces. The exercises are taking place in Russia's southern Astrakhan region, roughly 500 miles from the border with Ukraine.

Similar military exercises in the region preceded the annexation of Crimea.

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CNN's Susanna Capelouto and Catherine E. Shoichet reported from Atlanta. CNN's Phil Black reported from Moscow. CNN's Jim Acosta, Isa Soares and journalist Olga Pavlova contribute to this report.