Russia will take counter measures if Washington imposes new sanctions on Moscow over the Ukraine crisis, Russia's Deputy Foreign Minister Sergei Ryabkov said on Saturday.

The U.S. Congress has readied new sanctions on Russian weapons companies and investors in the country's high-tech oil projects, but U.S. President Barack Obama has yet to sign a corresponding bill into law.

"We will not be able to leave that without an answer," Russia's Interfax news agency quoted Ryabkov as saying. He did not say what form of counter-measure Moscow might take.

Relations between Russia and the United States are at their lowest since the Cold War because of Russia's annexation of Crimea from Ukraine in March and its support for pro-Russian rebels in eastern Ukraine.

The West says it has firm evidence that Russia has armed the rebels - an accusation that Moscow rejects - and has, together with the European Union, imposed several rounds of economic sanctions on Russian individuals and large companies.

Russia retaliated to the earlier sanctions by restricting food imports from a range of Western countries.

Russia on Friday criticised the Ukraine Freedom Support Act, which foresees further sanctions, saying Washington was doing its utmost to "destroy the carcass of cooperation" between the two countries. (Reporting by Alexander Winning; editing by Ralph Boulton)