Security forces say they have been following Hashem Abedi "for more than one month and a half"
A brother of suspected Manchester bomber Salman Abedi 'knew' of the plans and has been arrested in Libya, the country's security forces have claimed.
Hashem Abedi was held on Tuesday evening and is claimed to have known about his brother's plot to detonate a nail bomb at the end of a pop concert on Monday night.
22 people were killed in the attack at Manchester Arena, following an Ariana Grande show.
A spokesman for Libya's counter-terror force said: "We have evidence that he is involved in Daesh (Islamic State) with his brother.
"We have been following him for more than one month and a half. He was in contact with his brother and he knew about the attack."
Hashem, born in 1997, is suspected of planning to carry out an attack in Tripoli and travelled from London to the Libyan capital on April 16, the spokesman added.
There was no reason given for the arrest of Abedi's father Ramadan Abedi, after Reuters reported he was detained outside his home in a Tripoli suburb on Wednesday afternoon.
Ramadan had earlier insisted his son Salman was innocent of Monday's suicide bombing.
He said: "We don't believe in killing innocents. This is not us."
Meanwhile, five people have been arrested in the UK as the investigations into Monday's bombings continue.
Constable Ian Hopkins of Manchester Police said: "It's very clear that this is a network that we are investigating."
The UK's terror threat level remains at 'critical' - the highest level - following the attack.