In the unverified footage, a man wearing a mask and sitting in front of a black flag making the ominous warning.

The man then holds up a sign bearing the words “Manchester 2017-05-22”, a reference to yesterday’s date.

Hours later ISIS claimed responsibility for the attack via the Reuters news agency and the killer was named as Salman Abedi.

In the video the masked man says: “In the name of Allah the merciful, the grateful, this is only the beginning.

“The lions of the Islamic State are beginning to attack all the crusaders. Allahu akbar. Allahu akbar.”