Russia today gave US officials the names of four diplomats to be sent home and also explained what further steps it would take in retaliation for Washington's decision to send home 50 Russians.
A Foreign Ministry statement said Mr John Ordway, number two at the US embassy, had been given a note listing the four. The names were not made public.
The diplomats were declared personae non gratae and ordered to leave Russia within 10 days, because of activities incompatible with their diplomatic status, a standard diplomatic phrase for spying.
The note also stated the other measures being taken by the Russian side to halt the illegal activities of American special services in Russia , the statement said.
The US embassy, where Mr Ordway has been in charge while ambassador Mr James Collins is out of town, declined to comment.
Russia said last week it would expel the four in a tit-for-tat retaliation to a US expulsion of four Russians.
Washington has said it will also send home a further 46 Russians by July in the biggest spy row since the Cold War. Moscow says it will match the expulsions one for one.
Russia earlier responded with outrage in another simmering feud, calling Washington's decision to host a representative of Chechen separatist leader Aslan Maskhadov immoral.
Offering a solemn welcome to the envoy of the Chechen fighters, the new US administration showed with its trademark 'decisiveness' on what side of the international struggle against terrorism it stands, the Russian Foreign Ministry said.