Al-Shabab, the Somali armed group, has named Ahmed Umar, also known as Abu Ubaidah, as successor to Ahmed Abdi Godane who was killed in US airstrikes last Tuesday.

The armed group on Saturday pledged to take revenge for the death of one its founding leaders.

"Avenging the death of our scholars and leaders is a binding obligation on our shoulders that we will never relinquish nor forget no matter how long it takes," the group said in a statement sent to Al Jazeera.