FBI 'warned MI5 in January that Salman Abedi was planning terror attack in UK'

British intelligence agency MI5 was reportedly warned by its US counterpart that Salman Abedi was planning an attack on UK soil, three months before he blew himself up outside an Ariana Grande concert in Manchester.

FBI agents are said to have informed British officials that the 22-year-old was part of a North African Islamic State cell based in the north west of England that was plotting an attack in the UK.

Abedi was reportedly placed on a US terrorist watch list in 2016 after he came to the attention of intelligence agencies during an investigation into terrorist groups operating in Libya.

“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," a security source told The Mail on Sunday.

“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.”

MI5 has faced questions over the fact that Abedi was on its radar but slipped through the net in order to carry out the attack that killed 22 people and seriously injured 64.

In response, defence officials said that at any one time they are juggling 500 terror investigations involving 3,000 subjects.

37 show all Manchester explosion in pictures

1/37 People running down stairs as they attempt to exit the Manchester Arena after a blast, where U.S. singer Ariana Grande had been performing, in Manchester Twitter/@ZACH_BRUCE/ via REUTERS

2/37 Helpers attend to people inside the Manchester Arena after a suspected suicide bomber detonated an explosive device at the end of an Ariana Grande concert, killing 22 people PA wire

3/37 Armed officers guard outside a hotel near the Manchester Arena following reports of an explosion, in Manchester, Britain EPA

4/37 Police officers are seen outside the Manchester Arena, where U.S. singer Ariana Grande had been performing, in Manchester, northern England Reuters

9/37 Police and fans close to the Manchester Arena, after reports of an explosion Getty Images

10/37 There have been reports of explosions at Manchester Arena where Ariana Grande had performed Getty Images

11/37 Police deploy at scene of explosion in Manchester, England, at a concert in Manchester Arena AFP/Getty Images

12/37 Police stand by a cordoned off street close to the Manchester Arena Getty Images

13/37 Police deploy at scene of explosion in Manchester, England AFP/Getty Images

14/37 Police deploy at scene of a reported explosion during a concert in Manchester, England, on May 23, 2017. British police said early May 23 there were "a number of confirmed fatalities" after reports of at least one explosion during a pop concert by US singer Ariana Grande. Ambulances were seen rushing to the Manchester Arena venue and police added in a statement that people should avoid the area AFP/Getty Images

15/37 An ambulance drives away from the Manchester Arena, where U.S. singer Ariana Grande had been performing, in Manchester Reuters

16/37 Police escort members of the public from the Manchester Arena in Manchester, England. Getty Images

17/37 A woman sits in the street in a blanket near the Manchester Arena as police guard the area following reports of an explosion, in Manchester, Britain EPA

18/37 Two women wrapped in thermal blankets stand near the Manchester Arena, where US singer Ariana Grande had been performing, in Manchester Reuters

19/37 A Royal Logistic Corps (RLC) bomb disposal robot is unloaded outside the Manchester Arena following reports of an explosion, in Manchester. At least 19 people have been confirmed dead and others 50 were injured, authorities said. It is being treated as a terrorist incident until police know otherwise EPA

20/37 A Royal Logistic Corps (RLC) bomb disposal robot is unloaded outside the Manchester Arena following reports of an explosion, in Manchester EPA

21/37 Members of the public receive treatment from emergency service staff at Victoria Railway Station close to the Manchester Arena on May 23, 2017 in Manchester, England. There have been reports of explosions at Manchester Arena where Ariana Grande had performed this evening. Greater Manchester Police have have confirmed there are fatalities and warned people to stay away from the area Getty Images

22/37 Armed police after a suspected terrorist attack at the Manchester Arena at the end of a concert by US star Ariana Grande left 19 dead PA wire

23/37 Emergency services arrive close to the Manchester Arena in Manchester Getty Images

24/37 An amoured police vehicle patrols near Manchester Arena in Manchester Getty Images

25/37 A man carries a young girl on his shoulders near Victoria station in Manchester AFP/Getty Images

26/37 Police officers stand at the Miller Street and Corporation Street Crossroads, in front of the Manchester Arena in Manchester, England Getty Images

27/37 Police block a road near to the Manchester Arena in central Manchester, England AP

28/37 Armed police patrol near Victoria station in Manchester, northwest England. Twenty two people have been killed and dozens injured after a suspected suicide bomber targeted fans leaving a concert of US singer Ariana Grande in Manchester Getty Images

29/37 Police forensic officers leave the Manchester Arena as they investigate the scene of an explosion in Manchester Getty Images

30/37 A forensic officer collects evidence on a walkway between Victoria station and Manchester Arena following a deadly terror attack in Manchester, Getty Images

31/37 A woman and a young girl wearing a t-shirt of US singer Ariana Grande talks to police near Manchester Arena following a deadly terror attack in Manchester, Getty Images

33/37 Mayor of Greater Manchester Andy Burnham and Manchester City Council Leader Sir Richard Leese speak to the media outside Manchester Town Hall after a suicide bomber killed 22 people, including children, as an explosion tore through fans leaving a pop concert in Manchester Dave Higgens/PA Wire

34/37 The media gather behind a police cordon in Manchester Getty Images

35/37 Flowers left close to the Manchester Arena, the morning after a suicide bomber killed 22 people, including children, as an explosion tore through fans leaving a pop concert in Manchester Danny Lawson/PA Wire

36/37 Ariana Grande concert attendees Karen Moore and her daughter Molly Steed, aged 14, from Derby, leave the Park Inn where they were given refuge after last night's explosion at Manchester Arena Getty

37/37 Signs saying 'We love Manchester' are displayed in a window in Manchester, England Getty Images

Police have so far arrested 14 people on suspicion of terror offences in conjunction with the Manchester attack, two of whom have since been released.

Detectives believe they have detained “a large part of the network” involved in planning the attack.

The latest raid took place in Moss Side, a suburb of Manchester – close to the barber shop run by Abedi’s cousin that officers had previously searched.