UK security chiefs were warned in January that Salman Abedi was planning an attack in Britain, it was claimed last night.

According to a security source, the FBI told MI5 that Abedi was part of a North African Islamic State cell plotting to strike a political target in the UK.

The information came from a US investigation into Abedi and his links to terrorist groups in Libya. The Mail on Sunday has also been told that US security services put him on a terror watch list – used by agents to identify key suspects – in 2016.

Alert: Bomb disposal experts work with police in the Moss Side area yesterday as fresh arrests were made

The shocking claim piles further pressure on MI5 to reveal when and how it became aware of Abedi, and why UK spies decided he did not pose a significant threat to British security.

The 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.

Salman Abedi on the night that he travelled to the Manchester Arena and detonated a bomb after the Ariana Grande concert, killing 22 people and injuring 119

This photo shows the aftermath of the suicide bomb which ripped through the foyer of the venue killing parents and children

'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.'

Last night, The Mail on Sunday put the claim to the FBI but a bureau spokesman declined to comment, while UK security sources did not confirm the specific claim about the tip-off.