An American journalist said he had been banned from Russia after he reported on mass protests against Ukraine's scrapping of an EU pact.
The US Embassy in Moscow has been informed of the move against David Satter and has lodged a formal diplomatic protest, Radio Free Europe/Radio Liberty president and CEO Kevin Klose said. It has sought and not obtained an explanation from Russian authorities.
The move, coming on the eve of the Sochi Winter Olympics next month, was likely to further strain already tense ties between Washington and Moscow.
It was believed to be the first expulsion of a US journalist from Russia since the Cold War.
"I was told that my presence in Russia in the view of the security organs was undesirable. Other than that, no reasons were given," Satter told AFP via email from London.
"My belongings are in Moscow where I have an apartment. But without permission to enter the country, I cannot retrieve them. I would like to return to Moscow to work but cannot do so without a visa."
Satter had been living and working in Russia as an RFE/RL adviser since September 2013. He had also been reporting and providing commentary to the outlet's Russian service, in addition to providing interviews and analysis to other news and opinion websites.
"When he was trying to leave Ukraine from covering the protests to come back to Russia, that's when the problems started," RFE/RL spokeswoman Karisue Wyson said by telephone.
In December, Satter received notification that his visa request was approved, including an official Russian Foreign Ministry notification number, Wyson said.
But Satter was later told by a Russian Embassy official in Kiev that his presence in Russia was considered "undesirable" and his visa request was denied, according to Wyson.
On RFE/RL's website, Klose said he considers the use of the term "undesirable" to be the equivalent of declaring Satter "persona non grata" in Russia.
"We (RFE/RL) want nothing more than Mr Satter forthwith be able to return to Moscow, where he has lived and worked since September 2013, advising, reporting and commenting for our Russian Service and providing trenchant interviews, columns and analysis to many news and opinion sites," Klose said in a statement.