MANCHESTER, England -- Security forces rounded up more suspects Wednesday and early Thursday in the deadly Manchester concert blast and soldiers fanned out across the country to national landmarks as an on-edge Britain tried to thwart the possibility of additional attacks.

Officials scoured the background of the British-born ethnic Libyan identified as the bomber, saying he was likely part of a wider terrorist network. Additional arrests were made both in Britain and in Libya in the bombing that killed 22 people and wounded scores more.

Among those taken into custody in Libya were the suspected bomber's father and his younger brother, the latter of whom confessed to knowing "all the details" of the attack plot, Libyan anti-terror authorities said.

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Home Secretary Amber Rudd said the bomber, Salman Abedi, "likely" did not act alone in the attack. She said he had been known to security forces "up to a point."

"I think it's very clear this is a network we are investigating," said Greater Manchester Police Chief Constable Ian Hopkins, adding that an off-duty police officer was among those killed in the concert attack.

Police in Manchester raided properties believed to be connected to Abedi, arresting three men earlier Wednesday. Officers later arrested another suspect in the town of Wigan, west of Manchester, and were assessing a package the suspect was carrying. No one has yet been charged in the case and police have not identified the suspects.

The Greater Manchester Police tweeted an arrests update early Thursday:

Further update pic.twitter.com/t2F5cxyJXv — G M Police (@gmpolice) May 25, 2017

Abedi, a 22-year-old British citizen, grew up in the Moss Side district of Manchester. The neighborhood has been home to numerous individuals who have been convicted of terrorism charges or died fighting for terrorist groups overseas.

Government officials said nearly 1,000 soldiers were deployed to Buckingham Palace, Parliament and other high-profile sites across the country. Britain's terror threat level was raised to "critical" - the highest level - on Tuesday over concern another attack could be imminent.

French Interior Minister Gerard Collomb said Abedi was believed to have traveled to Syria and had "proven" links to the Islamic State group, which claimed responsibility for the attack. British officials, however, have not commented on whether Abedi had links to IS or other extremist groups.

British authorities were probing whether Abedi had ties to other cells across Europe and North Africa, according to two officials familiar with the case who spoke on condition of anonymity because they were not authorized to speak about the ongoing investigation.

They said one thread of the inquiry involved pursuing whether Abedi was part of a larger terror cell that included Mohamed Abrini, otherwise known as "the man in the hat," with connections to the Brussels and Paris attacks. Abrini visited Manchester in 2015.

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"It looks like we're not dealing with a lone wolf situation. There's a network - a cell of ISIS-inspired terrorists," said U.S. Rep. Mike McCaul, R-Texas, chairman of the House Homeland Security Committee. He said the bomb's construction suggested a "level of sophistication" that might indicate foreign training.

British police have arrested a seventh person in connection with the Manchester Arena bombing.

The man was held Wednesday after police carried out searches in the English town of Nuneaton, which is about 100 miles south of Manchester.

His arrest was the first in England to take place outside of Manchester since the bombing.

A woman who was arrested in Blackley, an area north of Manchester, was released early Thursday, police said. The other six people are still in custory, the Greater Manchester Police said.

The sprawling investigation extended to Libya, where Abedi's father and 18-year-old brother were detained in Tripoli. The father, Ramadan Abedi, denied his son had links to militants in an interview with The Associated Press before he was taken into custody, saying, "We don't believe in killing innocents."

The elder Abedi was allegedly a member of the al-Qaida-backed Libyan Islamic Fighting group in the 1990s, according to a former Libyan security official, Abdel-Basit Haroun.

The Libyan anti-terror force that arrested the men said in a statement that the brother, Hashim Abedi, 18, confessed that he and his brother were linked to the Islamic State group and that he was aware of the arena bombing plan. The anti-terror force said the father had not been charged, but was taken in for questioning.

A second brother, Ismail Abedi, 23, was taken into custody in Manchester a day earlier.

A soldier and police officer walk past the Houses of Parliament in London on May 24, 2017. Neil Hall/Reuters

The suspected bomber grew up in Manchester's southern suburbs and once attended Salford University there. Neighbors recalled him as tall, thin and quiet, and said he often wore traditional Islamic dress. Among investigators' areas of interest is how often Abedi traveled to Libya, which has seen an eruption of armed Islamist groups since dictator Moammar Gadhafi was overthrown and killed in 2011.

Before his arrest, Abedi's father said he had last spoken to his son five days ago and he sounded "normal." He said his son was getting ready to visit Saudi Arabia for a short Umrah pilgrimage then planned to head to Libya to spend the Islamic holy month of Ramadan with his family. He said his son last visited Libya about six weeks ago and had never gone to Syria. He denied ties to any militant groups or suggestions of extremism.

"We aren't the ones who blow up ourselves among innocents," he said. "We go to mosques. We recite Quran, but not that."

At Manchester's Didsbury Mosque, where the Abedi family worshipped, the bombing was condemned and reports that the suspected bomber had worked there were denied. Azhar Mahmoud, who prays at the mosque in southern Manchester, said it was "horrible" that Abedi was associated with it.

"Wherever he got that, he didn't get it from this mosque," he said, adding that the imam regularly preached against radicalization.

British Prime Minister Theresa May chaired a meeting Wednesday of her emergency security cabinet group to talk about intelligence reports on Abedi and concerns that he might have had outside support. Police raided homes believed to be connected with the investigation.

At one apartment building in Manchester, heavily armed police swarmed in and a controlled explosion was heard. Muye Li, a 23-year-old student who lives on the same floor, said he thought officers were looking for a woman because they "asked me if I had seen the lady next door."

At another property, a house a 10-minute walk from where Abedi lived, neighbors said they were awakened by a loud noise and saw a man hauled away in handcuffs.

Residents continued to place floral tributes to the dead and injured as police arrested a man at a house near Abedi's home.

Omar Alfakhuri, who lives across the street, said he was awakened at 2:30 a.m. by a loud noise and saw police take away the father of the family that lives there in handcuffs. He said the man, in his 40s, is named Adel and has a wife and several children.

"They arrested the father, and I think the rest of the family kind of disappeared," Khuri said, adding that he knew the man from the neighborhood and the mosque. "In the last 15 years, I haven't seen him in trouble at all."

At Manchester's Didsbury Mosque, where the Abedi family worshipped, authorities condemned the bombing and denied reports that Abedi had worked there. Azhar Mahmoud, who prays at the mosque in south Manchester, said it was "horrible" that the bomber was associated with it.

"Wherever he got that, he didn't get it from this mosque," he said.

Manchester Islamic Centre and Didsbury Mosque Trustee, Fawaz Al Haffar (C), gestrures as he addresses members of the media outside of Didsbury Mosque in Didsbury, Manchester, northwest England, on May 24, 2017. Oli Scarff/AFP/Getty Images

Mahmoud said the imam regularly preached against radicalization.

"He always tells the youngsters, stay away from it. ... I've prayed there Fridays, and that's his message."

British Prime Minister Theresa May chaired a meeting Wednesday of her emergency security cabinet group to talk about concerns Abedi might have had outside support. France's interior minister said Abedi is believed to have also traveled to Syria and had "proven" links with ISIS.

Rudd said Britain's increased official threat level will remain at "critical" until security services are convinced there is no active plot in place.

She also complained about U.S. officials leaking sensitive information about Abedi to the press, saying that could hinder Britain's security services and police.

"I have been very clear with our friends that that should not happen again," she said.