The younger brother of the Manchester bomber was involved in a plot to attack a UN special envoy in Libya, it has been reported.

Hashim Abedi was a member of a jihadi cell that targeted Martin Kobler, the head of the United Nations Support Mission in Libya, during a visit to Tripoli earlier this year, sources told The Sunday Telegraph.

The 20-year-old was arrested by Libyan counter-terrorism forces on Tuesday, a day after his brother, Salman Abedi, killed 22 people blowing himself up at Manchester Arena.

Security services in the North African country said they had been monitoring Hashim for more than a month and that he had confessed he knew about Monday night’s atrocity.

Ahmed Bin Salem, a spokesman for Rada, the Libyan Special Deterrence Force, added: “We have evidence that he is involved in Daesh [Isis] with his brother.”

Hashim was alleged to be a “significant player” in the terror cell that planned to attack Kobler and the group was said to be in the late stages of building an explosive device to bomb the German national’s convoy in Tripoli.

But the plot was interrupted by security forces before it could be carried out, The Telegraph reported.

Hashim Abedi told Libyan authorities he shared ideology with his brother (AFP/Getty) (AFP)

Hashim was arrested at his family home in Tripoli along with his father, Ramadan Abedi.

The younger brother admitted to interrogators he had had links to Isis, a spokesman for Libyan authorities told BBC Two’s Newsnight.

The spokesman said: “We were not quite sure about this, but when we arrested and we asked him, he told us, ‘I have ideology with my brother’. Hashim told us, ‘I know everything about my brother, what he was doing there in Manchester’.”

He added Hashim had told authorities that 22-year-old Salman had learned to make explosives on the internet.

The Telegraph, with the help of investigative website Bellingcat, said it had uncovered Hashim’s deactivated Facebook account, on which he had referred to Osama Bin Laden as his “hero” and liked a picture of a plane flying into the World Trade Centre in New York.

He was shown in one photograph as a teenager holding a machine gun.

The newspaper claimed social media accounts suggested there was a network of young, radicalised men in Manchester, Cardiff and Portsmouth, who discussed support for Isis and other terrorist groups.

Greater Manchester Police has taken 12 people into custody on suspicion of terror offences since the suicide bombing following an Ariana Grande concert.

Salman Abedi had learned to make explosives on the internet (PA/GMP)

A 25-year-old man held in the Old Trafford area of the city was the latest to be arrested, on Sunday.

On Saturday, two men aged 20 and 22 were detained after officers used an explosive device to gain entry to a property in Cheetham Hill.

The head of national counter terrorism policing said “immense” progress had been made in the probe into the associates of Salman Abedi and a “large part” of his suspected network had been dismantled.

Mark Rowley added: “They are very significant, these arrests.

“We are very happy we’ve got our hands around some of the key players that we are concerned about but there’s still a little bit more to do.”