British police investigating the deadly concert bombing in Manchester earlier this year said Wednesday they had requested the extradition of the attacker's brother from Libya.

Salman Abedi killed 22 people when he detonated a suicide bomb after a concert by pop star Ariana Grande, Britain's worst terror attack in more than a decade.

Manchester-born to Libyan parents, Abedi is believed to have travelled to Libya in the run-up to the May 22 bombing.

Greater Manchester Police said they have now gathered enough evidence to request and be granted an arrest warrant for the attacker's brother, Hashem Abedi.

"The arrest warrant relates to the murder of 22 people, the attempted murder of others who were injured and conspiracy to cause an explosion.

"Hashem Abedi is currently detained in Libya and the CPS (Crown Prosecution Service) has now requested that Libyan authorities consider his extradition back to the United Kingdom.

"We are grateful for the Libyan authorities considering this request," said the force's Russ Jackson, who is also head of counter terrorism in north-west England.

In total 112 people were hospitalised following the Manchester Arena bombing, two of whom remain in hospital.

In the days following the bombing, one of the forces that supports Libya's UN-backed unity government posted a picture on its Facebook page of Hashem Abedi after detaining him.

"The father, Ramadan Abedi, has also just been arrested," said Ahmed bin Salem, a spokesman for the Deterrence Force, which acts as Government of National Accord's police.

Manchester police did not provide details on whether the duo had been continuously held since May, or whether they had been released and subsequently detained.