Moscow - Russian diplomats expelled from the United States arrived in Moscow on Sunday, with post-Cold War tensions peaking in the wake of a nerve agent attack on a former spy in Britain.
A deepening crisis in ties between Russia and the West has over the past weeks seen the biggest wave of tit-for-tat diplomatic expulsions in recent memory.
In further signs of tension, Russia warned its nationals on Saturday to think twice before travelling to Britain, where it said they could be singled out for harassment by local authorities.
By expelling 60 Russian diplomats, the US joined a score of Britain's allies in responding to the poisoning of former double agent Sergei Skripal and his daughter Yulia in the English city of Salisbury on March 4.
Two planes arrived at Moscow's Vnukovo airport on Sunday, bringing home a total of 171 people -- the 60 diplomats and their families -- from Washington and New York.
Russian television showed passengers disembarking from a government plane while several buses waited to pick them up.
More than 150 Russian diplomats have now been ordered out of the US, EU members, NATO countries and other nations.
Britain has said it is "highly likely" that Russia was responsible for the Skripal attack using the Soviet-designed Novichok nerve agent. Russia has angrily denied any involvement.
The US alleged the 60 diplomats were "spies" and sent them home from posts around the country and at the Russian mission to the United Nations, as well as closing Russia's consulate in Seattle.
However Washington has since said that Russia is free to apply to accredit more diplomats to replace those expelled.
Moscow responded by expelling 60 US diplomats and closing Washington's consulate in Saint Petersburg on Saturday.
-- 'Work to improve ties' --
US President Donald Trump has often appeared reluctant to criticise Russian leader Vladimir Putin and has said the two could meet for a summit in the near future.
"Now the consulate is closed but our work to improve Russian-US ties is continuing," the US embassy in Moscow said on Twitter.
Moscow also issued further retaliatory measures against Britain on Saturday, demanding that London further slash its diplomatic presence.
"Russia suggested parity. The British side has more than 50 more people," foreign ministry spokeswoman Maria Zakharova told AFP.
The call came after 23 British diplomats were expelled from Russia last month.
Moscow also closed a British consulate in Saint Petersburg and suspended all projects of the British Council for the first time in nearly 60 years.
- 'Threatening rhetoric' -
The Russian embassy in London urged Russians to think carefully before travelling to the UK or sending children to summer school there.
The embassy warned that British authorities including police could single out Russians for additional checks, citing "the anti-Russian policies and an escalation of the British side's threatening rhetoric".
Britain acknowledged Saturday that border officials had searched an incoming Aeroflot flight from Moscow in what Russia blasted as an act of "blatant provocation".
Britain said it conducts routine checks on aircraft to protect the UK from organised crime and people attempting to bring harmful substances into the country.
Earlier this week Moscow summoned British ambassador Laurie Bristow, giving London a month to cut the number of diplomatic staff in Russia to the same number Russia has in Britain.
He was handed a protest note over the "provocative and unfounded actions of the British side which instigated the unwarranted expulsion of Russian diplomats from a variety of states," the Russian foreign ministry said.
Bristow was summoned along with the heads of missions from 23 other countries -- most of them EU member states -- who were told that some of their diplomats had to leave.
France, Germany, Canada and Poland each said that Russia was expelling four of their diplomats.
Other countries including Australia, Ukraine, the Netherlands, Sweden, the Czech Republic, Finland, Lithuania and Norway were also told to pull their envoys.