Al-Shabaab, an Al-Qaeda-affiliated group, has been waging a deadly insurgency against the fragile central government in Somalia for more than 17 years.

UN resolutions called for forces in the African Union peacekeeping mission, known as ATMIS, to be reduced to zero by December 31 through several withdrawal phases, handing over security to the Somali army and police.

The third and penultimate phase was to see the departure of 4,000 soldiers by the end of June.

However, an AU official who requested anonymity told AFP that in May, the Somali government asked the organisation's Peace and Security Council (PSC) to extend the presence of half of the troops by three months.

The government wants only 2,000 men to leave in June and the other 2,000 in September, the official said, adding that Mogadishu had put forward the need to carry out an "offensive operation".

At present, 13,500 ATMIS soldiers are deployed in Somalia.

Meeting on Thursday in Addis Ababa, the PSC was expected to give a favourable response, said the source.

"The PSC will discuss on Thursday the (Somali) request to slow down the reduction in the number of ATMIS troops by a few months," an AU diplomat, who also requested anonymity, told AFP.

But any extension would lead to budgetary problems, he said, and a change would not be "just a decision by the PSC".

ATMIS derives its mandate from the AU but must also be authorised by the UN Security Council.

In addition, ATMIS' main direct financial contributor is the European Union, which has released 70 million euros ($75 million) for 2024.

Comprising troops from Burundi, Djibouti, Ethiopia, Kenya and Uganda, ATMIS supports the Somali army, which has been fighting Al-Shabaab for over 17 years.

Although driven out of the capital by AU forces in 2011, Al-Shabaab still has a strong presence in rural Somalia.

It has carried out repeated attacks against political, security and civilian targets, mostly in Somalia but also in neighbouring countries including Kenya.

Last week in southern Somalia, Al-Shabaab planted a roadside bomb that killed six soldiers including a senior military commander.