RUSSIA has warned its citizens against visiting Britain due to the threat of "inevitable" new terrorist attacks.

Vladimir Putin's government issued the travel advice after the UK raised its threat level to "critical" - the maximum possible - following the killing of 22 in this week's Manchester bombing.

6 Russia's Foreign Ministry Spokesperson Maria Zakharova giving a briefing on the current Russian foreign policy and international relations last month Credit: Getty Images

6 People gather to look at the flowers and tributes left in St Ann's Square in Manchester after the terror attack Credit: Getty Images

6 Soldiers joined armed police to guard Westminster and other key areas in London this week as security was stepped up countrywide Credit: EPA

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".

It comes as tens of thousands of young Russians are due to visit Britain for annual language summer schools.

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Earlier, Foreign Ministry spokeswoman Maria Zakharova stopped short of advising against travel to the UK after Salman Abedi detonated a nail bomb in the Manchester Arena on Monday night.

"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.

The embassy said the British secret services had advised further terror attacks "are inevitable", and 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 were urged to follow official announcements on new threats, follow media advice, avoid crowds and be "very careful" using public transport.

6 Armed police began patrolling the UK's train networks for the first time yesterday Credit: PA:Press Association

6 A sea of flowers and tributes have been laid in the days following the horrific attack in Manchester Credit: AP:Associated Press

6 Salman Abedi blew himself up, killing 22 people at Ariana Grande's concert Credit: AP:Associated Press

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'.

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 megalopolis cities.

"Having called army to patrol the infrastructure is a sign of a very serious situation.

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"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.

Abedi may have been given a crucial component for his device at a German airport en route to his terror mission, it has been revealed.

Security officials are checking CCTV for possible contact between the 22-year-old and terror suspects in Dusseldorf.

Immediately after the attack police began a desperate race to find the bomb gang behind the Manchester Arena massacre on Monday night.

A total of ten people have now been arrested over the devastating attack, with two released without charge and eight still in custody.