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. As many as 3,800 will be available to back up police operations in following waves of deployment, UK Home Secretary Amber Rudd said.
Abedi grew up in Manchester's southern suburbs and once attended Salford University there. All four men are now in police custody. Authorities were raiding properties thought to be connected to Abedi.
Numerous 22 victims were children and young adults, the youngest of which was eight years old.
Officials are examining Abedi's trips to Libya as they piece together his allegiances and try to foil any new potential threats.
Soldiers carrying SA-80 rifles walked alongside uniformed officers outside the Houses of Parliament, Buckingham Palace, Downing Street and other important sites.
Experts at the Joint Terrorism Analysis Centre raised the threat level to "critical" - the highest on the scale - as police worked to identify further conspirators.
The Metropolitan Police said the incident, which happened at around 10.40am on Wednesday, is not believed to be terror-related. Abedi's brother, 23, was arrested on Tuesday.More news: Marking difference with U.S., France urges dialogue with Iran
Heavily armed police raided an apartment building in Manchester on Wednesday afternoon, blasting the door open with a controlled explosion.
I would like to confirm that we are confident that we have now spoken to all the immediate families of those who sadly died in Monday's attack and they are all now being supported by specially trained officers.
The changing of the guard ceremony at Buckingham Palace was canceled Wednesday so police officers can be re-deployed, Britain's defense ministry said.
One thousand extra armed police officers are being deployed across the United Kingdom, the Met Police has said. Armed police also patrolled outside St. Paul's Cathedral in London.
The Chelsea soccer team announced it would cancel Sunday's victory parade in London that was to have celebrated the team's Premier League title win this season.
Police Federation chairman Steve White said the Government must ensure there is a "resilient, fully-resourced police service", adding: 'We the police simply do not have the resources to manage an event like this on our own'.
Poland's Foreign Ministry confirmed on Wednesday that at least two Polish citizens died and one was among the 59 injured in the attack at the end of a concert by U.S. singer Ariana Grande in the northern English city. We are using this to help in our efforts enable the Manchester Games and Manchester 10k to go ahead.More news: South Korea Wants to Reopen Communication With North
Security forces are urgently trying to establish whether the bomber had accomplices.
He denied having ties to any of Libya's militant groups, including the Libya Islamic Fighting Group, which was linked to al-Qaida. Although the LIFG disbanded, Haroun says the father now belongs to the Salafi Jihadi movement, the most extreme sect of Salafism from which al-Qaida and the Islamic State group both hail.
"I have asked for support from the military to be deployed alongside the police ..." Rudd said Britain's operational security could be harmed by the leaks, taking "the element of surprise" away from security services and police. He said the man is named Adel and is in his 40s, with a wife and several children.
"There was a policeman, armed policeman, shouting", neighbor Omar Alfa Khuri said.
He said he knew the man from the neighborhood and the mosque but "in the last 15 years, I haven't seen him in trouble at all".
Rudd also confirmed in a media interview Wednesday that she had spoken to Washington after premature details emerged in the US media about the identity of the suicide bomber who detonated a device at the Manchester Arena.More news: CBO: 23 million fewer Americans insured under House GOP bill
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