An injured Kenyan soldier steps out of a plane after arriving in Nairobi, Jan. 17, 2016, following Friday's attack by al-Shabab on an African Union base in southwest Somalia. John Muchacha/AFP/Getty Images

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. The Islamist group claimed to have killed more than 100 Kenyan soldiers so far and captured many others, Agence France-Presse reported.

Al-Shabab, which is aligned with al Qaeda, attacked the remote army compound in southwest Somalia early Friday after a suicide bomber rammed its gates. The terrorist group said it was also in control of the small, neighboring town of Ceel Cado.

"We embarked on a search, rescue and recovery operation as a priority," Gen. Samson Mwathethe, Kenya's military chief, told reporters Sunday in a press statement. "Our troops are engaging the terrorists."

Kenyan officials have declined to say how many of its soldiers were killed, injured or missing following the attack in Somalia. But al-Shabab said more than 100 Kenyan soldiers were killed, AFP reported.

The insurgents "stormed the Kenyan base in the early hours of Friday morning, killing more than 100 Kenyan invaders, seizing their weapons and military vehicles and even capturing Kenyan soldiers alive," said an email statement cited by AFP.

Reliable figures are tough to come by. Al-Shabab often exaggerates the number of soldiers it kills while the AU Mission in Somalia (AMISOM) and Kenyan government officials often downplay the tolls, AFP reported.

Kenya said Sunday it was leading a search-and-rescue mission in southwest Somalia after al-Shabab seized an African Union Mission in Somalia base. Pictured: AMISOM officers patrol around the Gashandhiga academy compound, April 12,2015, in Mogadishu. Mohamed Abdiwahab/AFP/Getty Images

African Union forces, which total around 22,000 soldiers from several African countries, have spent nearly a decade fighting al-Shabab forces in Somalia. In the last year, the terrorist group has launched multiple guerrilla-style attacks on AMISOM bases to drive out foreign troops and impose its severe version of Islamic law throughout the region.

AMISOM and the Somali army have managed to drive al-Shabab out of major strongholds in the country. But the group still controls some rural areas and stirs up instability with its ambushes and bomb attacks on military bases.

Al-Shabab said in a statement its Friday attack on the Somali base "sends a clear message to the Kenyan government that their military's invasion of our Muslim lands and the massacre of innocent Muslims perpetrated by the Kenyan crusaders will not be without severe consequences," Reuters reported Friday.

Mwathethe vowed to continue pushing back against al-Shabab. "We will fight them deep in their hideouts, we will smoke them out of their caves and we will follow to the end in honor of every drop of blood of our Kenyans," he said in the Sunday statement. "Our resolve to combat terrorism remains."