Daesh terrorist group claimed the London subway explosion late Friday.

The group, via its affiliated Amaq agency, stated that the explosion was perpetrated by an "affiliated unit."

The bomb exploded on a packed train during rush hour on Friday, leaving at least 22 people injured but no one seriously hurt. Police said the explosion was a terrorist attack, the fifth in Britain this year.

Witnesses described seeing a "wall of fire" as the bomb — hidden in a plastic bucket inside a supermarket freezer bag — went off about 8:20 a.m. while the train was at the Parsons Green station in southwest London.

The site of the blast is in a leafy, affluent part of the city, not near any of London's top tourist sites. British media reported that the bomb included a timer. It's not clear whether the device was intended to explode when it did.