Ethiopian Prime Minister Hailemariam Desalegn has said Ethiopia is "anxious" to pull its forces out of Somalia "as soon as possible" and called on the African Union force in the country to speed up its deployment.

Answering questions by members of parliament, Hailemariam said the main issue for Ethiopia was "to accelerate our complete withdrawal towards our border" with Somalia, a statement on the Ethiopian foreign affairs ministry website said.

He expressed concern at the slow pace at which the African Union force AMISOM, which first deployed in 2007, is replacing the Ethiopians.

Unlike other regional governments, whose forces are part of AMISOM -- Uganda, Kenya, Burundi, Djibouti, and more recently Sierra Leone -- Ethiopia's are not and their deployment costs are not covered by the AU.

The Ethiopian troops crossed into southwestern Somalia in November 2011 and have been decisive in routing the Shebab extremists and maintaining control over areas clawed back from their control.

But in mid-March, Ethiopia pulled its troops from the southern town of Hudur without warning, leading to the Shebab immediately taking back the town, their first real military success since they were chased out of Mogadishu in August 2011.

The surprise and unexplained withdrawal from Hudur caused speculation that Ethiopia was starting a wider pullout from Somalia and sparked fears that it would lead to a security void and a possible return of the Shebab.

Hailemariam recently promised the Somali authorities that his troops would pull out only once they had been replaced by AMISOM forces.

Several observers questioned by AFP said that AMISOM likely does not have sufficient troops to replace the Ethiopians, whose numbers are estimated to be between 3,000 and 8,000 men.

Hailemariam on Wednesday in Nairobi met with Kenyan President Uhuru Kenyatta, whose country is one of the main contributing nations to AMISOM.