Twenty-three expelled Russian diplomats and their families have left London for Moscow as Britain and Russia traded recriminations over a nerve agent attack in England that has plunged relations into their worst crisis since the Cold War.
Prime Minister Theresa May blamed Russia for the attack on a Russian double agent and his daughter 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 Sergei Skripal and his daughter and, in a reciprocal gesture on Saturday, gave 23 British diplomats a week to leave Moscow as well as closing the British Council in Russia.
A state-owned Russian Ilyushin-96 plane made a special flight from Moscow to London's Stansted airport to pick up the diplomats who were given a warm send-off by Russia's top diplomat in London.
Russia has refused to explain how Novichok, a nerve agent first developed by the Soviet military, was used to strike down Skripal, a former colonel in Russian military intelligence who betrayed dozens of spies to Britain.
Skripal, 66, and his 33-year-old daughter 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 two sides continued to exchange accusations over the affair.
Russian diplomats told the Conference on Disarmament at the United Nations in Geneva that Britain may have produced the toxin itself and that Moscow did not owe any explanations.
Britain's ambassador to the forum, Matthew Rowland, said Russia had given misleading statements on its Novichok program.
Putin, who was elected for a fourth term in the Kremlin on Sunday, said Russia had been falsely accused.
"As for the tragedy that you mentioned, I found out about it from the media. The first thing that entered my head was that if it had been a military-grade nerve agent, the people would have died on the spot," Putin told reporters on Sunday.
"Secondly, Russia does not have such (nerve) agents. We destroyed all our chemical weapons under the supervision of international organisations, and we did it first, unlike some of our partners who promised to do it, but unfortunately did not keep their promises," Putin said.
A Cold War-era scientist acknowledged on Tuesday he had helped create the nerve agent, contradicting Moscow's insistence that neither Russia nor the Soviet Union ever had such a program.
However, Professor Leonid Rink told the RIA news agency that the attack did not look like Moscow's work because Skripal and his daughter had not died immediately.
Australian Associated Press
