MANCHESTER, England (ABC News) - Three more arrests have been made in connection with the deadly explosion at an Ariana Grande concert in Manchester, England, Monday, that killed 22 people including children, authorities said today.
The suspects were apprehended in south Manchester early this morning, according to the Greater Manchester Police.
Police also announced Tuesday that they had arrested a 23-year-old man in connection with the attack.
The news of three more arrests comes one day after U.K. Prime Minister Theresa May raised the country's threat level to critical -- the highest of the United Kingdom's five threat levels -- indicating that another attack could be imminent.
Investigators on Tuesday identified 22-year-old Salman Abedi as the suspected suicide bomber behind the fatal explosion. He died at the scene. Police said they were investigating if Abedi acted alone or with a group.
ISIS has since claimed responsibility for the bombing.
Saffie-Rose Roussos, 8, is the youngest known victim of the bombing. She was separated from her mother and sister, who were among the wounded, police said.
The mother of 15-year-old Olivia Campbell confirmed on Facebook that her daughter was among those killed.
Runshaw College in Lancashire confirmed on its Facebook page that 18-year-old student Georgina Bethany Callander died from her injuries sustained in the attack. Callander's former school in Lancashire, Bishop Rawstorne Church of England Academy, also confirmed her death.
Lisa Lees, a 43-year-old mother and grandmother, was confirmed to be among the dead by her daughter, Lauren Ashleigh Lees.
"My mum was an amazing lady and wife," her daughter said in a statement. "We will pull together as a family and help each other through the darkness."
On Wednesday police in London said that the public should expect to "see more armed officers" patrolling the streets in response to the elevated terrorist threat levels.
"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," the Metropolitan Police Service said in a statement. The law enforcement agency said it would "continually change" the number of officers deployed as well as the officers' posts and tactics in an attempt to avoid predictability.
"The reality is that 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," Metropolitan Police Service Commander Jane Connors said in the statement. "That is why is we have increased the number of firearms who are on duty, both out walking and in roaming patrols, at fixed points and carrying out a range of operations."
Amid the security developments, the U.K. Ministry of Defense announced that the Changing the Guard ceremony at Buckingham Palace had been canceled for Wednesday in order to allow police officers to be redeployed.