Reuters adds:

"Islamic State, in a statement posted on a messaging service it uses, said it detonated a car laden with explosives aimed at Saad's convoy in Aden's Tawahi district and promised more operations against 'the heads of apostasy in Yemen.' A local official and residents said earlier on Sunday a suicide bomber rammed his vehicle into the governor's car.

"The group's local branch has stepped up operations since the outbreak of civil war in Yemen, emerging as a forceful rival to Al Qaeda in the Arabian Peninsula (AQAP), the main militant group in the country in recent years."