Russia has ordered the United States to cut hundreds of diplomatic staff in retaliation for a new round of US sanctions, and said it was seizing two US diplomatic properties.
Moscow's decision, which had echoes of the Cold War, was announced by the Foreign Ministry a day after the US Senate overwhelmingly approved new sanctions on Russia. The legislation was in part a response to conclusions by US intelligence agencies that Russia meddled in the 2016 US Presidential election, and to further punish Russia for its annexation of Crimea in 2014.
The Bill now goes to President Donald Trump, who could give it final approval or veto it.
Russia had been threatening retaliation for weeks. Its response suggests it has set aside initial hopes of better ties with Washington under Mr Trump, something the US leader, before he was elected, had said he wanted to achieve.
Relations were already languishing at a post-Cold War low because of the allegations that Russian cyber interference in the election was intended to boost Mr Trump's chances, something Moscow flatly denies. Mr Trump has denied any collusion between his campaign and Russian officials.
The Russian Foreign Ministry complained of growing anti-Russian feeling in the United States, accusing "well-known circles" of seeking "open confrontation".
President Vladimir Putin had warned on Thursday that Russia would have to retaliate against what he called boorish US behaviour. Putin's spokesman, Dmitry Peskov, told reporters on Friday that the Senate vote was the last straw.
A top White House aide said on Thursday that Trump might veto the bill in order to push for a tougher deal, an idea that drew scepticism in Congress because his administration had spent weeks lobbying for a weaker bill. The bill is expected to garner enough support in both chambers to override any veto.
Russian foreign minister Sergei Lavrov told US Secretary of State Rex Tillerson by telephone that Russia was ready to normalise relations with the United States and to cooperate on major global issues.
Lavrov and Tillerson "agreed to maintain contact on a range of bilateral issues", the Russian Foreign Ministry said.
The ministry said the United States had until September 1 to reduce its diplomatic staff in Russia to 455 people, the number of Russian diplomats left in the United States after Washington expelled 35 Russians in December.
It was not immediately clear how many US diplomats and other workers would be forced to leave either the country or their posts, but the Interfax news agency cited an informed source as saying "hundreds" of people would be affected.
A diplomatic source told Reuters that it would be for the United States to decide which posts to cut, whether occupied by US or Russian nationals.
An official at the US Embassy, who declined to be named because they were not allowed to speak to the media, said the Embassy employed around 1,100 diplomatic and support staff in Russia, including Russian and US citizens.
Russian state television channel Rossiya 24 said over 700 staff would be affected but that was not confirmed by the foreign ministry or the US embassy.
The Russian Foreign Ministry's statement said the passage of the bill confirmed "the extreme aggression of the United States in international affairs".
"Hiding behind its 'exceptionalism', the United States arrogantly ignores the positions and interests of other countries," it said.
"Under the absolutely invented pretext of Russian interference in its domestic affairs, the United States is aggressively pushing forward, one after another, crude anti-Russian actions. This all runs counter to the principles of international law."
Deputy Foreign Minister Sergei Ryabkov met outgoing US ambassador John Tefft on Friday to inform him of the counter measures, Russian news agencies reported. The US Embassy said Tefft had expressed his "strong disappointment and protest".
Most US diplomatic staff, including around 300 US citizens, work in the main embassy in Moscow, with others based in consulates in St Petersburg, Yekaterinburg and Vladivostok.
The Russian Foreign Ministry said it was also seizing a Moscow dacha compound used by US diplomats for recreation, from August 1, as well as a US diplomatic warehouse in Moscow.
Last December, the outgoing Obama administration seized two Russian diplomatic compounds - one in New York and another in Maryland - at the same time as it expelled Russian diplomats.
Mr Putin said at the time that he would wait to see how Mr Trump handled the issue before responding, and Mr Trump praised his restraint.
The two men met for the first time at a G20 summit in Germany this month in what both sides described as a productive encounter, but Russian officials have become increasingly convinced that Congress and Mr Trump's political opponents will not allow him to mend ties, even if he wants to.
"The adoption of the new sanctions law showed clearly that relations with Russia have become hostage to a domestic political battle in the United States," the Foreign Ministry said.
The ministry warned it would respond in kind if Washington decided to expel any more Russian diplomats.
The European Union has also threatened to retaliate against new US sanctions on Russia, saying they would harm the bloc's energy security by targeting projects including a planned new pipeline to bring Russian natural gas to northern Europe.
A European Commission spokesman in Brussels gave a non-committal response to the Senate vote, saying: "We will be watching how this process unfolds and then of course we will be watching equally attentively how this law, if and when it enters into force, will be applied in practice."