Somalia's lawmakers have approved the appointment of new Prime Minister Abdiweli Sheikh Ahmed, who vowed to appoint a larger and more effective cabinet.

Ahmed, an economist, previously worked at the Islamic Development Bank in Saudi Arabia. He replaces Abdi Farah Shirdon who was forced out by lawmakers in a vote of no confidence after falling out with President Hassan Sheikh Mohamud.

Western donors had worried a prolonged vacuum at the head of government would interrupt efforts to rebuild state institutions and defeat al Qaeda-linked militants who control swathes of the rural south and centre of the Horn of Africa country.

The speaker said 243 of the 248 members of parliament voted with a show of hands in favour of Ahmed. The speaker abstained.

"My government will work with parliament and other government institutions. I will appoint a larger and more effective cabinet soon. My government will improve security, health, education and reconstruction," Ahmed said after being sworn in.

President Mohamed Siad Barre's overthrow in 1991 plunged Somalia into turmoil, first at the hands of clan warlords and then Islamist militants, who have steadily lost ground since 2011 under pressure from an African Union military offensive.-Reuters