TAKE HEART KDF survivors are received by Defence CS Raychelle Omamo and CDF Samson Mwathethe at Wilson Airport yesterday

Kenya said it was leading a search-and-rescue mission Sunday at an African Union base in Somalia after al-Shabab fighters overran the facility two days earlier.

Kenya has not given casualty figures beyond saying both sides sustained casualties. The operation is "delicate" because some Kenyan soldiers have been captured and are being used as human shields, he said.

The Shebab frequently exaggerates the number of troops they kill, while AMISOM rarely gives exact tolls.

Somali troops and Kenyan soldiers with the AU force, AMISOM, are deployed at the isolated base. On Sunday four injured soldiers were returned to Nairobi.

The soldiers who belonged to 9th Kenya Rifles Formation in Eldoret were said to have been on their second tour of Somalia.

After receiving training, Ahmed and Yusuf travelled to Mogadishu, where they fought in a series of brutal battles alongside other USA and European fighters who had joined al Shabaab to take control of the city in 2009, prosecutors said.

The Shebab, fighting to overthrow Somalia's internationally-backed and AU-protected government, has lost much territory in Somalia but continues to launch attacks there as well as in Kenya, killing at least 67 people at Nairobi's Westgate Mall in 2013 and massacring 148 people at a university in Garissa last April.

The El Adde attack was carried out by suicide bombers using improvised explosive devices on vehicles and "the soldiers affected by the attack are a company size force", Defence Secretary Raychelle Omamo said in a separate statement on the Ministry of Interior's website.

The responsibility for the attack had been immediately claimed by the Somali militant group, Al Shabaab, which is considered a terrorist organization by the US. But al-Shabab said more than 100 Kenyan soldiers were killed, AFP reported.

Somali and Kenyan military officials said the fighters had seized the Somali army base near the town of Ceel Cadde, about 550 km (340 miles) west of Mogadishu in a region near Kenya's border.