Twenty three expelled Russian diplomats and their families left the embassy in London and headed back to Moscow on Tuesday following the first known offensive use of a nerve toxin in Europe since World War Two.
Prime Minister Theresa May blamed Russia for the attack on Sergei Skripal, a Russian double agent, and his daughter Yulia, and gave 23 Russians whom she said were spies working under diplomatic cover one week to leave London.
Russia has repeatedly denied any involvement in the attack on Skripal and his daughter and on Saturday gave 23 British diplomats a week to leave Moscow as well as closing the British Council in Russia.
Three buses with diplomatic number plates left the Russian embassy compound in London on Tuesday morning, a Reuters photographer at the scene said. Embassy workers waved to the leaving diplomats as the buses pulled away.
Skripal, 66, and 33-year-old Yulia have been critically ill since they were found unconscious on a bench in the English city of Salisbury on March 4. A British policeman who was also poisoned is in a serious but stable condition.
Russia says it knows nothing about the poisoning and has repeatedly asked Britain to supply a sample of the nerve agent that was used against Skripal.
The United States and European powers say they share Britain's belief that Russia is culpable for the poisoning though they given no indication of what they will do about it.
EU leaders will say this week that they will "coordinate on the consequences" for Russia after the poisoning, according to a draft summit statement seen by AFP.
The 28 leaders meeting in Brussels on Thursday will wait to see what answers Moscow provides on the nerve agent attack, the draft says.
The draft however makes no overt mention of sanctions or any other diplomatic measures to follow the lead of Britain.
