Sky.com reports: “We know who they are, we have found them,” Mr Putin said at an economic forum in the Russian city of Vladivostok.

“There is nothing special or criminal about it, I can assure you.”

“I would like to call on them so that they can hear us today,” said Mr Putin.

“They should go to some media outlet. I hope they will come forward and tell about themselves.”

Hours later Russian state TV announced one of the men would be breaking their silence next week.

Theresa May said it was not a “rogue operation” and their actions were “almost certainly also approved outside the GRU at a senior level of the Russian state”.

Police published a detailed photographic account of the men’s movements while in the UK.

It named them as Ruslan Boshirov and Alexander Petrov but said those names were probably false.

An Interpol “red notice” and a European arrest warrant have been issued for their arrest should they ever try to leave Russia.

Russia never extradites its citizens so the UK government did not bother asking. The Kremlin refused to extradite Andrei Lugovoi, the suspect in the 2006 Alexander Litvinenko poisoning.

Former Russian double agent Sergei Skripal and his daughter Yulia were found slumped on a bench in Salisbury in March this year.

Tests found they had been poisoned with the deadly nerve agent novichok.

The Skripals recovered but British woman Dawn Sturgess died after finding a discarded perfume bottle that authorities believe was used to transport the novichok.

A spokesman for Prime Minister Theresa May said Britain has “repeatedly asked Russia for an explanation of Salisbury” but was “always met with obfuscation and lies”.