LONDON, May 24 (Xinhua) -- Armed soldiers have been deployed guarding Buckingham Palace, 10 Downing Street, the Houses of Parliament and foreign embassies, police in the British capital said Wednesday.

The announcement came as police in Manchester announced that three men had been arrested in the city as part of their inquiries into the Monday suicide bombing at the Manchester Arena which left 22 people dead.

It brings to four of those being held after a 23-year-old was arrested Tuesday.

In response to the raising of the country's terror threat to critical, the highest level, the Metropolitan Police said it has increased police numbers and operations across London with immediate effect to guard against international terrorism.

"The public will see more armed officers, working alongside their neighborhood and specialist colleagues on proactive operations and targeted patrols, both on foot and in vehicles," said the Met in a statement.

Armed officers will provide support to teams of specialist police officers who have been trained to spot the tell-tale signs that a person may be carrying out hostile reconnaissance or committing other crime, the Met added.

"The approach is based on extensive research into the psychology of criminals and what undermines their activities," said a spokesman.

Soldiers will now be working under Met command to provide static armed guarding at key locations, said the spokesman. This will include Buckingham Palace, Downing Street, Embassies and the Palace of Westminster.

Police Commander Jane Connors, leading the London policing operation, said: "We must be prepared to be able to respond to and deal with armed and deadly attackers, so we must be in a position to respond with firearms officers who will use force to stop those attackers in their aim."