The Bush administration is publicly calling on Moscow to honor Britain's extradition request and officials here say it is backing that up with similar advice in contacts with Russian officials.
British authorities have named a Russian businessman, Andre Lugovoi, as the chief suspect in the poisoning death in London last November of former KGB agent Alexander Litvinenko, who was an outspoken critic of the Russian government.
After Russia refused Britain's extradition request, the government of the new British Prime Minister Gordon Brown retaliated this week by ordering the expulsion of four Russian diplomats.
Moscow Thursday ordered the reciprocal expulsion of four British diplomats and also said it was halting anti-terrorism cooperation with London.
Though it has cultivated good relations with Moscow, the Bush administration Thursday came out in unequivocal support for NATO ally Britain in the case.
Echoing comments by Secretary of State Condoleezza Rice in Lisbon, State Department Deputy Spokesman Tom Casey said the poisoning of Litvinenko with radioactive polonium was a horrible crime for which justice must be done:
The perpetrators of that crime should be brought to justice. And this is something that we believe is not only in the interest of justice in the broader sense, and in the interests of the U.K. but also in the interests of Russia. Nobody wants to see murderers get away with their crime, and it's important for Britain to be able to learn the truth about what happened in this case. But it is important as well for Russia to see that justice is served.
Casey said the case has been raised in U.S. diplomatic dealings with Moscow, but stopped short of saying the affair has had a negative impact on the bilateral relationship with Russia, which he said is fundamentally constructive.
Secretary Rice also urged Russian cooperation with Britain in the murder case during an interview in Lisbon, where she joined Russian Foreign Minister Sergei Lavrov and others in a meeting of the international Middle East Quartet.
Rice told Britain's Sky TV she does not think the Litvinenko case and resulting political fall-out signals a return to the Cold War. She said Russians live in greater freedom than they did under the Soviet Union, and that the United States has wide areas of cooperation with Russia on, among other things, counter-terrorism and nuclear non-proliferation including the cases of Iran and North Korea.
At the same time, Rice said there are complexities in the relationship including disappointing progress in Russia on democracy, regression on press freedom, and what she suggested was a tendency by Moscow use its energy resources as a political tool. She advised dialogue on problem issues with Moscow rather than trying to paper them over, and said there is nothing to be gained by the isolation of Russia.