The Somali Islamic extremist group al-Shabab says it captured some Kenyan soldiers during its attack Friday on a base of African Union peacekeepers in southwestern Somalia.

On Sunday four wounded Kenyan soldiers were airlifted back home but Kenyan officials gave no death toll.

Kenyan Defense Secretary Raychelle Omamo told reporters that there is an ongoing search, rescue and recovery operation in the area where the attack happened.

In a statement Sunday, al-Shabab claimed the number of dead Kenyan troops had risen to 100. It was not possible to verify that figure.

The al-Shabab statement also said that its fighters seized armaments and military vehicles.

Al-Shabab, which opposes Kenya's military involvement in Somalia and describes the Kenyans as invaders, has carried out many deadly attacks inside Kenyan territory.