Somali President Mohamed Abdullahi Mohamed has appointed political newcomer Mohamed Hussein Roble as the country's prime minister, hours after brokering an agreement with regional leaders for elections next year that abandons a promised one-person, one-vote model.

In a statement late on Thursday, the president's office wished Roble "to take duties and tasks ahead with diligence".

Mohamed, who is usually referred to by his nickname of "Farmaajo", is likely to run for a second term as president when polls are held, competing against at least two other former presidents.

Roble studied civil engineering and previously worked for the International Labour Organisation, a United Nations agency.

He will replace former Prime Minister Hassan Ali Khaire, who was voted out of office by parliament in July for failing to pave the way for fully democratic elections due before February 2021.

The United Nations had described the pursuit of one-person, one-vote elections as an "historic milestone" on Somalia's path to full democratisation and peace after decades of war and violent instability.

But observers had warned that such a goal was looking increasingly unlikely due to tensions with the states, technical aspects such as voter registration, and security challenges posed by the al-Qaeda-affiliated al-Shabab armed group.

The fragile central government, chaired by Farmaajo, controls only part of Somali territory and relies on an international peacekeeping force to confront an armed campaign from al-Shabab in the countryside.

Mogadishu had been criticised by observers for engaging in political feuds with federal states to gain control in the election process, rather than focusing on the fight against the armed group.