The first of a group of 60 US diplomats who have been expelled from Russia in the wake of the poisoned spy row departed from Washington's embassy in Moscow early Thursday, an AFP reporter on the scene said.
Dozens of US diplomats and their families left the embassy compound on three buses and a minibus at 6.30am (0330 GMT) and headed towards the airport, after Moscow set a Thursday deadline for the envoys to leave the country.
There has been a flurry of tit-for-tat diplomatic expulsions since the March 4 poisoning on UK soil of Sergei Skripal, which Britain says was carried out with a military-grade nerve agent developed by the Soviet Union.
The former double agent, who defected to Britain, was found slumped on a park bench in the English town of Salisbury alongside his daughter Yulia who was also critically injured.
London has said it is "highly likely" Moscow was behind the botched assassination, a charge the Kremlin has angrily denied.
Relations between Moscow and the West have since plummeted to a new lows.
More than 150 Russian diplomats were ordered out of the US, EU members, NATO countries and other nations as punishment, a move that was met in kind by Russia.
At the end of March Moscow ordered 60 US diplomats to leave, as well as the closure of the St Petersburg consulate.
There was a stream of vehicles driving in and out of the embassy ahead of the departure, many carrying luggage and the pets of the expelled diplomats.