Terrorist's family arrested as police hunt Manchester bomb maker

Police have arrested further suspects as they try to track down the potential bomb maker responsible for the Ariana Grande concert suicide blast that killed 22 people and injured at least 119.

Police have now arrested a total of seven suspects in Libya and Britain, including the father and brother of the man believed to have carried a bomb in his backpack into Manchester Arena, as the attack was linked to a wider terrorist network.

Libyan authorities said special forces had arrested the brother of Salman Abedi, the suspected Manchester attacker, on Tuesday.

Hashem Abedi, the alleged attacker's brother, confessed that he and Salman Abedi were both members of the Islamic State extremist movement, according to a statement by Libyan special forces on Facebook.

Despite the arrests, UK authorities believe the person responsible for making the backpack bomb might still be at large.

Hashem Abedi also said he had visited Britain to help prepare the Manchester attack and he was "clearly aware of the details of this terrorist operation," the statement said.

He had been under surveillance since he left Britain in mid-April and had remained in constant contact with Salman Abedi, it said.

Ramadan Abedi, the father of Salman, was arrested near his home in Tripoli, Libyan authorities said.

Their arrests come as police in Britain detained four more suspects linked to Salman Abedi.

"I think it's very clear that this is a network that we are investigating," Greater Manchester Police Chief Constable Ian Hopkins told reporters when asked whether police are looking for a possible bomb maker.

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Hopkins declined to elaborate and gave no details about Wednesday's three arrests in south Manchester and one in the town of Wigan, 25 kilometres from Manchester.

The Wigan suspect was carrying a package which the police were investigating, police said, without giving further details. The most recent arrest was a woman at a Manchester block of flats.

Police announced the arrest of the first suspect, a 23-year-old man rumoured to be the older brother of the attacker, on Tuesday.

The Times, citing CCTV footage recovered by police, said Salman Abedi had placed a suitcase in the foyer of the concert hall shortly before the explosion.

Hashim Abedi (left) is the 18-year-old brother of suspected Manchester bomber Salman Abedi. Source: AP

The newspaper quoted a friend as saying Abedi, who died in the explosion, had returned to Britain from Libya just days before the attack.

British and French officials said earlier Wednesday that Abedi probably had accomplices and had links to Islamic State.

French Interior Minister Gerard Collomb said Abedi had been "radicalised" and had probably travelled to Syria during a trip to Libya.

Prime Minister Theresa May raised Britain's terrorism threat level to the highest level of "critical" late Tuesday, meaning a further attack is likely or "imminent."

Armed police will increase patrols and military personnel will be deployed at events such as concerts and sports matches.

Grande has cancelled all upcoming concerts through to June 5 following the bombing, a statement from her manager said.