The US Federal Bureau of Investigation warned UK security chiefs in January that Salman Abedi was planning an attack in Britain.

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, Daily Mail reported.

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.

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 suicide bombing happened on May 22 following a pop concert by the US singer Ariana Grande. At least 22 people, including 12 children, were killed, 66 were receiving hospital treatment, some as outpatients, and 23 people remained in critical care. In addition, nine people, most of whom are teenagers, are considered missing.