Russia banned most meat imports from the United States early last year because of concerns over the use of the feed additive ractopamine. The country previously planned to resume pork imports from the United States from around March 10.

"Imports from these two plants will be resumed as soon as the issue with refrigerators, from which supplies are due to come, is resolved," VPSS spokesman Alexei Alekseenko said.

"I can't say if it's going to happen before March 10, it depends on the U.S. side," he added.

Russian news agencies reported earlier on Tuesday that the decision by VPSS to ask for more guarantees meant that Russia had put its decision on U.S. pork imports on hold.

Alekseenko said that their interpretation was wrong.

"We still plan to allow pork imports from two Smithfield firms. This list can be broaden in future," he said.

U.S. pork producer Smithfield Foods Inc was bought by China's Shuanghui International Holdings last year.

Russia's decision to use military forces in Ukraine's Crimea region has drawn strong criticism from Western countries including U.S. President Barack Obama who said on Monday that the U.S. government would look at economic and diplomatic sanctions to isolate Moscow.

(Reporting by Polina Devitt; editing by Jason Neely)