LONDON, May 24 (Xinhua) -- A minute's silence is to take place across Britain Thursday to honor the victims of the Manchester Arena attack.
Queen Elizabeth II's decision for the tribute at 11 a.m. local time was announced by Buckingham Palace.
Hours before the announcement, troops arrived at the palace to take up guard duty as part of a response to Monday's bombing which left 22 dead.
In Manchester, police announced a fifth arrest in connection with Monday's attack at the end of a concert by American pop star Ariana Grande.
A police spokesman said: "We have made an arrest in Wigan (an industrial town north of Manchester) in connection with the investigation into the horrific incident at Manchester Arena. When arrested, the man was carrying a package which we are currently assessing."
One eyewitness told the media that the man had been held in a swoop by undercover armed police. He said workers in nearby offices had been told to stay inside and lock their windows, and a red package had been moved to a clear part of the street.
With the country's terror threat level raised to "critical," the highest level, around 1,000 soldiers have been deployed guarding key buildings, including 10 Downing Street, the Houses of Parliament and foreign embassies.
As more heartbreak details emerged of victims of the suicide bombing in Manchester on Monday, police carried out raids in the Manchester area, bringing the total held for questioning to five.
Ian Hopkins, Greater Manchester police chief constable revealed Wednesday that suicide bomber Salman Abedi was almost certainly part of a terror network.
It sparked a race to seek and detain other members of a potential terror cell amid fears of further attacks and bombings.
Hopkins said: "I think it's very clear that this is a network that we are investigating."
He said the investigation which left 22 dead, the youngest aged just 8, and 64 injured, was "continuing at a pace".
With London Mayor Sadiq Khan urging people in the British capital to stay calm, more security measures were taken. The Houses of Parliament were closed to visitors and one of the highlights for sightseers in London, the traditional Changing of the Guard ceremony at Buckingham Palace, was called off.
Home Secretary Amber Rudd said the arena attack was more sophisticated than some of the attacks seen before in Britain.
She told media in London it seemed likely that the suicide bomber Abedi wasn't "doing this on his own."
Media in London were reporting that Abedi returned to Britain from Libya a few days before Monday night's attack in Manchester.
In the wake of the heightened terror threat, Chelsea football club cancelled a victory parade, planned for Sunday in London, to celebrate winning the English Premier League.
Meanwhile campaigning in the general election, ahead of voting on June 8, is expected to resume later this week after being suspended following the bombing. Jeremy Corbyn, leader of the main opposition Labour Party, said further delays to campaigning would undermine democracy.