Salman Abedi is believed to have planned Monday’s terror attack in Manchester for at least a year
MI5 were reportedly told by the FBI that Abedi was part of a North African Islamic State cell plotting to strike a political target in Britain.
The information is reported to have come from a US investigation into Abedi and his ties to terror groups in Libya.
In 2016, it was alleged that US security services put Abedi on a terror watchlist used by agents to identify key suspects.
The claim is likely to increase pressure on MI5 to reveal how and when it became aware of Abedi.
It also comes at a time where there are questions over why UK spies decided Abedi did not pose a significant threat to British security.
A source told the Mail on Sunday: “In early 2017 the FBI told MI5 that Abedi belonged to a North African terror gang based in Manchester, which was looking for a political target in this country.
“The information came from the interception of his communications by US federal agents, who had been investigating Abedi since the middle of 2016, and from information unearthed in Libya, where his family was linked to terrorist groups.
“Following this US tip-off, Abedi and other members of the gang were scrutinised by MI5. It was thought at the time that Abedi was planning to assassinate a political figure.
“But nothing came of this investigation and, tragically, he slipped down the pecking order of targets.”
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The FBI reportedly warned UK security services about Abedi's terror ambitions
UK security services refused to confirm the specific claim about the tip-off.
Abedi is believed to have planned Monday’s terror attack in Manchester for at least a year.
Abedi’s sister, Jomana, has suggested he carried out the attack in response to US air strikes in Syria.
She said: “I think he saw children — Muslim children — dying everywhere, and wanted revenge.
"He saw the explosives America drops on children in Syria, and he wanted revenge. Whether he got that is between him and God.”
The Manchester bombing killed 22 people
The Manchester bombing killed 22 people and injured at least 59 others at an Ariana Grande concert.
UK security agencies are reported to have thwarted five terror plots aimed at UK citizens since the Westminster terror attack in March.