Moscow demands return of 'spy' compounds in the US
Russia says it is "outrageous" that the US has not yet handed back two Russian intelligence compounds seized in the US under the Obama administration.
The BBC has reported that the country's Foreign Minister, Sergei Lavrov, said he was "considering specific measures" in response, but did not elaborate.
Earlier, unnamed Russian officials said Moscow was ready to expel about 30 US diplomats and seize US state property. In December the Obama administration expelled 35 Russian diplomats and shut two suspected intelligence compounds.
Ex-President Barack Obama acted against Russia after US intelligence sources had accused Russian state agents of hacking into Democratic Party computers to undermine Hillary Clinton's presidential campaign.
Mr Lavrov said it was "simply shameful for such a great country as the United States, a champion of international law, to leave the situation in such a state of suspended animation".
"Justice and international law must be restored," he said, accusing the US Congress of being "charged up with Russophobia".
The US seized a Russian diplomatic property in Maryland - a sprawling 45-acre retreat.
The facility, acquired during the Cold War, was used by diplomats for recreation, such as tennis and swimming. But it also had sophisticated communications, and US officials said it doubled as a spying outpost.
The other diplomatic property is a New York mansion at Glen Cove, Long Island. It has 49 rooms and is similarly surrounded by woods. Like the Maryland mansion, its location is ideal for eavesdropping on US communications, US officials say.
Russian President Vladimir Putin raised the issue of the Obama sanctions with US President Donald Trump when they met in Hamburg last week, the daily 'Izvestia' reported.
But should Trump hand back the compounds, he will cement his image of Kremlin stooge in the eyes of his opponents. At this point any concessions to Russia would be highly controversial, in light of investigations in America into alleged links between Mr Trump's team and Moscow.
Yet if they are not returned, Moscow may well expel a number of US diplomats and seize some US diplomatic buildings. That could complicate what Mr Trump says he wants to achieve: better relations with Russia.
This is not the first time that reports have emerged of Russia planning counter-measures. The latest threat - via a foreign ministry source in a pro-Kremlin newspaper - may be designed to increase pressure ahead of US-Russia talks on the issue.
The Obama sanctions came on top of existing Western sanctions imposed because of Russia's role in the Ukraine conflict.
Mr Putin refrained from tit-for-tat retaliation - unlike in previous diplomatic spats. Mr Trump had been elected to succeed President Obama just weeks before.