The Ugandan military says it is searching for a number of its helicopters which have gone missing.

The helicopters were part of a group which was scheduled to make a stop in the Kenyan town of Wajir, but only one did so.

It is not clear how many helicopters have gone missing, nor how many people were on board.

The aircraft were part of a contingent being sent to reinforce the African Union peacekeeping force in Somalia.

"The search is going on, we don't know what exactly happened but we are investigating it," Ugandan military spokesman Felix Kulayigye told Reuters.

Ugandan troops are part of the African Union force fighting the Somali Islamist group al-Shabab, which pledges loyalty to al-Qaeda.

The force has been planning to launch an "onslaught" against al-Shabab in the Somali port of Kismayo later this month.

Al-Shabab has staged deadly attacks in Uganda, which is the largest contributor to the peacekeeping force. A double suicide attack in 2010 killed 76 people watching the football World Cup final.