Sudanese President Omar al-Bashir has appointed a top aide as prime minister, reinstating a post he abolished after coming to power in a 1989 coup, an official said.

Bakri Hassan Saleh will be sworn in on Thursday and immediately start negotiations on forming a new cabinet, said ruling National Congress Party deputy leader Ibrahim Mahmoud.

Saleh will hold onto his current post of Sudan's first vice president, Mahmoud said.

Sudanese lawmakers voted in December to reinstate the post of prime minister.

Saleh was among the officers who launched the bloodless 1989 coup, and the last member of the group to remain at Bashir's side.

The retired army general is a former defence, interior and presidential affairs minister. He currently serves as first vice president and National Congress Party deputy leader for executive affairs.

The naming of a prime minister and delegation of some of the president's powers fall in line with reforms proposed by a year-long national dialogue held between Bashir's government and some opposition groups.

In October, after a quarter century in power, Bashir concluded the national dialogue aimed at resolving insurgencies in Sudan's border regions and healing the country's crisis-wracked economy.

The process was boycotted by most mainstream opposition and armed groups.