Russia says it will respond harshly to any US measures designed to hurt it, a day after the United States told Moscow to close its San Francisco consulate and buildings in Washington and New York.
The warning on Friday, from Foreign Minister Sergei Lavrov, came as Russia said it was weighing a response to the US move that will force it to shutter two trade missions in the United States as well as the San Francisco consulate by September 2.
"We'll react as soon as we finish our analysis," Mr Lavrov told students in Moscow.
"We will respond harshly to things that damage us."
Separately, a top Kremlin aide complained the US pushed bilateral ties further into a blind alley and fuelled a spiral of tit-for-tat retaliatory measures.
US President Donald Trump took office in January, saying he wanted to improve US-Russia ties which were at a post-Cold War low.
But since then, ties have frayed further after US intelligence officials said Russia had meddled in the presidential election, something Moscow denies.
Mr Trump, himself battling allegations his associates colluded with Russia, grudgingly signed new sanctions on Moscow into law this month which had been drawn up by Congress.
When it became clear those measures would become law, Moscow ordered the United States to cut its diplomatic and technical staff in Russia by more than half, to 455 people.
Mr Lavrov hinted on Friday Russia might look at ordering further reductions in US embassy staff, suggesting Moscow had been generous last time by allowing Washington to keep "more than 150" extra people.
Mr Lavrov said Moscow still hoped for better relations and blamed Trump's political foes for the deteriorating situation.