The United States has criticised a Russian move to ban the import of US beef, pork and turkey.
The ban, which went into effect on Monday, has been in the works for weeks. Russian officials said it would last until the US could guarantee that its exported meat did not include an animal feed additive called ractopamine.
The additive is banned in the European Union and Russia, but the US considers it safe.
"The United States is very disappointed that Russia has taken action to suspend all imports of US meat, which is produced to the highest safety standards in the world," said Ron Kirk, the US trade representative, and Tom Vilsack, and US agriculture secretary in a joint statement.
Russia's move threatens a US meat export market worth more than $500m annually, raising suspicion that the ban is mainly intended to protect Russian livestock producers from a flood of cheap meat after joining the World Trade Organisation.
Many also see the action as retaliation after the US Congress passed legislation in December to punish Russian human rights violators.
The Russian ban also comes amid tensions over a US law imposing sanctions on Russian officials accused of rights violations. Russia retaliated by banning US adoptions of Russian children.
The Russian news agency Interfax on Monday quoted Gennady Onishchenko, the head of Russia's consumer safety watchdog, as saying he expected the "ban on practically all US meat and meat products will be long term".