Russians have been warned about the dangers of visiting the UK following the Manchester bombing
Vladimir Putin's government issued the travel advice based on its assessment of British secret services analysis over the likelihood of further incidents after the killing of 22 in this week's Manchester bombing.
But the Russians also suggested that the "growing influence of Islamic radicalism" among Muslim groups in British cities was a factor in a rising terrorist threat, and Theresa May's decision to call in the army showed a "very serious situation".
"The Russian embassy in Great Britain recommends Russian citizens refrain from travelling to the country, especially from visiting major cities, if such trips are not absolutely necessary," said the country's state tourism agency.
"This is due to the fact that the government of Great Britain has raised the level of the terrorist threat in the country to the maximum possible."
Travel advice from Russia's embassy in London says the country's citizens should "refrain from trips to Great Britain, especially from visiting metropolises, unless such trips are dictated by extreme necessity".
We recommend that Russian citizens refrain from visiting mass public events
Foreign Ministry spokesman Maria Zakharova
It comes as tens of thousands of young Russians are due to visit Britain for annual language summer schools.
Earlier, Foreign Ministry spokesman Maria Zakharova stopped short of advising against travel to the UK.
"We recommend that Russian citizens refrain from visiting mass public events and crowded places in British metropolises unless this is dictated by extreme personal or official necessity," she said.
Army bomb disposal unit called in Police raid in Manchester
Thu, May 25, 2017
Police have called in the Army bomb disposal squad at a raid in Hulme, Manchester. This is the first deployment of British troops in terror-related investigations
Get Quotes on Home Insurance
1 of 6
Army bomb disposal teams arrive in Hulme, South Manchester
The embassy said that the British secret services had advised that further terror attacks "are inevitable", and that the advice not to travel to the UK would remain until "the situation is stabilised by the state authorities", and the threat level lowered.
Russians already in Britain are urged to follow official announcements on new threats, follow media advice, avoid crowds and be "very careful" using public transport.
An anonymous diplomat added: "The British government has raised the level of terror threat to 'critical'….the fifth level of a 5 level scale.
"It supposes that, as the secret services say, terror attacks are 'inevitable in the coming future'.
A Foreign Ministry spokesman advised Russians stay away from crowded places unless necessary
The diplomat warned that the centres of major cities were vulnerable to attacks.
"Within the last three months the terrorist activity is only growing in the country," said the diplomat.
"We do not exclude that this is due to the growing influence of Islamic radicalism in the national communities who live in British megapolis cities.
The presence of the army on the street was pointed to as a reason for the warning
"Having called army to patrol the infrastructure is a sign of a very serious situation.
"Because the next act of terror is 'inevitable in the coming future', we do not have any other choice but to recommend Russians to refrain from visiting the UK until the situation is fully under control and the level of threat is officially decreased, unless such trips are extremely important due to business or personal reasons".
Russians in Britain were asked to "understand" that the authorities might carry out tougher checks.
"Be particularly concerned about the safety of your children," Russians were told.