A US drone strike in southern Somalia has killed Adnan Garaar, an al-Shabaab leader believed to be behind a 2013 attack on a Nairobi shopping mall that killed 67 people, the Pentagon has said.

It said in a statement that the strike last Thursday hit a vehicle carrying Garaar, a top official of the al-Shabaab armed group, which the Pentagon says targets US and other Western interests to further al-Qaeda's goals.