Brother of Manchester bombing suspect knew an attack was coming, Libyan official says Monday night's attack killed 22 people.

 -- The brother of Salman Abedi, the suspect accused of carrying out a bombing in Manchester, England, that killed 22 people, allegedly said he knew his brother was going to carry out an attack, but did not know where or when, according to a spokesman for Libya's counterterror forces.

Abedi, 22, the suspected suicide bomber, died at the scene of Monday night's attack at an Ariana Grande concert.

Authorities found what was described to ABC News as a bomb-making workshop in Abedi's home in Manchester, with enough chemicals to build several additional bombs.

Libyan authorities had been following Hashem Abedi, the suspect's brother who was born 1997, for a month and a half because of suspected links to ISIS, said Ahmed Dagdoug, the spokesman for Libya's counterterror forces. ISIS claimed responsibility for the attack.

The two brothers were close, and Dagdoug said that Salman placed a call to Hashem, as well as their mother, 30 minutes before carrying out the attack.

On Tuesday, that brother was detained in Libya. During interrogation, Hashem Abedi revealed that he knew his brother was going to carry out an attack, but he did not know where or when, Dagdoug said.

Dagdoug said Hashem Abedi also revealed that he knew exactly how the bomb was made, and that he believes that Salman created the device by himself. He said that he provided some assistance to his brother, but added no specific details as to what that was.

Dagdoug said a network was involved in planning the attack.

The brothers came to Libya on April 18 and Salman Abedi departed on May 17, Dagdoug said.

It's not clear at this time if Salman went to Syria, Dagdoug said.

Salman Abedi's father, Ramadan Abedi, was also arrested in Libya.

Ramadan Abedi was interviewed by Reuters from Libya while in detention, and he denied that his son was a follower of ISIS, who claimed responsibility for the attack on Tuesday.

"Salman doesn't belong to any organization," he told the news agency. "The family is a bit confused because Salman doesn't have this ideology, he doesn't hold these beliefs."

Dagdoug told ABC News that the two brothers do consider themselves to be members of ISIS and said that they had been studying ISIS videos online, including instructional videos that teach the viewer how to make a bomb.

Another one of the suspect's brothers, 23-year-old Ismail Abedi, was arrested in Manchester, a security official confirmed to ABC News.

A total of eight men have been taken into custody in the U.K. in connection with the attack. A woman who was arrested earlier was released without charge, police said.

Under British law, a person can be taken into custody in a terrorism investigation and held up to 14 days without being charged.

Chief Constable Ian Hopkins of the Greater Manchester Police said on Wednesday, "This is clearly a network that we are investigating, and extensive activity is taking place across Greater Manchester as we speak."

U.K. Prime Minister Theresa May on Tuesday raised the country's threat level to critical -- the highest of the U.K.'s five threat levels -- indicating that another attack may be imminent.

The U.K. Metropolitan Police said 1,000 additional armed officers have been freed up to carry out patrols across the U.K.

"The extra officers add to a wider policing plan which sees increased patrolling at crowded places, iconic sites and transport hubs as police and partners do everything they can to protect the public," the police said.

Witness Joseph Harries told ABC News' "Good Morning America" that "people were just trying to get out of the arena as fast as they possibly could after the blast. I was directly in front of the stage at the heart of the arena. I had exactly the same distance to get out of any of the doors."

"I had my best friend with me, and I grabbed hold of her wrist and told her never let go of me," he said. "We just ran. We jumped over chairs, railings to get out of the doors. We had to force open doors that wouldn't open because people were trying to get to -- the entire capacity of the 20,000-person arena were trying to get out of one exit.

"It felt like an eternity," Harries added, but it "couldn't have been more than two, three minutes from in our seats to outside of the arena."

Officials said that 119 people went to hospitals after the bombing, 64 of them are being treated and 20 of those are in critical condition.

Saffie Rose Roussos, 8, is the youngest known person who died from the attack. She was separated from her mother and sister, who were among the wounded, police said.

Fifteen-year-old Olivia Campbell was also among those killed, Campbell's mother wrote on Facebook.

Runshaw College in Lancashire confirmed on its Facebook page that 18-year-old student Georgina Bethany Callander died in the attack.

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."

Another victim was Nell Jones, who was in Year 9 at the Holmes Chapel Comprehensive School & Sixth Form College in Holmes Chapel, England.

"Nell’s family have been searching for her since the incident in the hope that they would find her being cared for in hospital. Unfortunately, the police have now confirmed that Nell died at the scene," the school headmaster, Denis Oliver, said in a statement. "We are all devastated by the loss and as a school community we must now come to terms with what has happened."

A sixth victim was identified as Martyn Hett, according to his employer at Rumpus PR.

“We are all distraught at the tragic loss of our much-loved, larger than life, colourful and charismatic colleague Martyn Hett," Rumpus PR Managing Director Paul Evans said in a statement. "Martyn was an upbeat and positive soul who saw the good, the joy, the fun in everything.

"At work, he was the consummate professional. A master of his subject -- he was a talented writer, creative thinker and social media expert," Evans added. "Martyn loved life and I hope his lasting legacy is that people -- in these dreadful times -- choose to live their lives with joy not hate, just like he did.”

Two more victims were identified as Chloe Rutherford, 17, and Liam Curry, 19. "On the night our daughter Chloe died and our son Liam died, their wings were ready by our hearts were not," the families said in a statement posted on the Greater Manchester Police Twitter account.

A school receptionist, Jane Tweddle, was also killed in the attack. "Jane was a well-loved member of staff and our thoughts are with her friends and family at this terrible time," Jane Bailey, principal of South Shore Academy, said in a statement. "We have received numerous messages of condolences from parents, students, community members and colleagues across Blackpool for which we are very grateful. All of them say the same things about our lovely Jane ... bubbly, kind, welcoming, funny, generous ... the list goes on."

And Allerton High School in Leeds confirmed that student Sorrell Leczkowski was killed, as well. "Sorrell was a delightful member of the school community," read a statement from the school. "She enjoyed her studies, had a lovely group of friends and was a real asset to Allerton High School."

On Tuesday, May said, "We struggle to comprehend the warped and twisted mind that sees a room packed with young children not as a scene to cherish but as an opportunity for carnage."

A moment of silence was observed Wednesday before Manchester United's Europa League final soccer game against Ajax Amsterdam. Manchester beat Amsterdam 2-0 to win the Europa League.