"We can confirm that an officer at our US embassy in Moscow was briefly detained and was released," State Department spokesman Patrick Ventrell told reporters.
"We've seen the Russian foreign ministry announcement and we have no further comment at this time," he said, added under repeated questioning that "I don't have anything more for you on the details of the case."
Russia said on Tuesday it had ordered the expulsion of an alleged American CIA agent working undercover at the US embassy who was discovered with a large stash of money trying to recruit a Russian agent.
Russia's Federal Security Service (FSB, ex-KGB) identified the man as Ryan C. Fogle -- third secretary of the political section of Washington's embassy in Moscow -- and said he had been handed back to the embassy after his detention.
State Department officials have been in contact with US ambassador to Russia Michael McFaul, who has been summoned by Russian authorities on Wednesday to provide an explanation of the case.
And Ventrell hinted more details might be provided after McFaul's meetings, but also refused to discuss whether Washington might be thinking of taking any tit-for-tat measure.
The diplomatic row comes as Russia and the US are trying to restore badly frayed ties, with US Secretary of State John Kerry due to meet his Russian counterpart Sergei Lavrov later Tuesday on the sidelines of talks in Sweden.
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