Russian diplomats ousted from London; Kremlin demands evidence

March 20 (UPI) -- Twenty-three Russian diplomats and their families left Moscow's embassy in London Tuesday, after they were expelled over the poisoning of former Russian double agent.

Russian state media reported that around 80 people left the embassy in minivans to the sound of the Proshchaniye Slavyanki patriotic march before heading to Moscow on a special flight.

The diplomats were expelled by British Prime Minister Theresa May last week as retaliation against Moscow for a nerve agent attack on Sergei Skripal, a 66-year-old former colonel in Russia's military intelligence service, and his 33-year-old daughter, Yulia.

British Foreign Secretary Boris Johnson said it was "overwhelmingly likely" that Russian President Vladimir Putin ordered the attack on Skripal.

The United States, Germany, France and the European Union echoed Britain's statements, placing the blame on Russia for the attempted murder of the Skripals.

The Kremlin has repeatedly denied any involvement in the attempted poisoning -- and has demanded British officials either show proof that Russia was responsible or apologize.

"Sooner or later they will have to be responsible for these allegations: they will either have to provide some evidence or apologize," Kremlin Spokesman Dmitry Peskov said Monday, calling Britain's accusations "difficult to explain" and "groundless and slanderous."

Peskov added Tuesday that Russians should remain "cool-headed" and wait for British officials to provide "evidence" concerning the poisoning.

"Putin has repeatedly stated that Russia has no connection to this case -- the possible attempted murder of the British spy in the U.K.," Peskov said. "Saying the opposite would be nonsense. Russia has no chemical weapons supplies, as they were destroyed, including under control of international observers and in strict compliance with Russia's international obligations."

In retribution, Moscow said it would also expel 23 British diplomats and close the British Council, an organization for cultural education and educational opportunities. The Russian Foreign Ministry also said the Kremlin is ending an agreement to reopen the British consulate in St. Petersburg.

The Kremlin said further measures would be taken if "more hostile actions" were taken against Russia.

The diplomat exchange marks the biggest tit-for-tat expulsions since former British Prime Minister Margaret Thatcher ordered Soviet spies to leave in 1985.