MOGADISHU, Somalia -- Kenyan troops were killed when al-Shabab Islamic fighters attacked an African Union base in Somalia, Kenya's president said Friday. He gave no casualty figure but an al-Shabab spokesman said at least 63 soldiers died.

President Uhuru Kenyatta described the loss as heartbreaking.

"Regrettably, some of our patriots in uniform paid the ultimate price," he said in a statement. "I want to take this opportunity to express mine and the country's deepest sympathy to the families and loved ones of the fallen. I stand with you. Our country stands with you."

Al-Shabab spokesman Abdiaziz Abu Mudan said on the group's online radio that at least 63 soldiers were killed in the attack in southwestern Somalia that started early Friday.

It happened in the town of El-Ade, not far from the Kenyan border. Kenya has provided a major contingent to the AU force that is fighting al-Shabab, a Somali Islamic extremist group linked with al Qaeda, and assisting the elected government of Somalia.

Francisco Madeira, the special representative of the African Union Commission for Somalia, condemned the attack, saying late Friday the casualties and injuries were still being verified.

Somali military official Ahmed Hassan, speaking to The Associated Press by phone from Elwak, a nearby town, said the attack started with a suicide car bomb, and then heavy gunfire was heard as militants stormed onto the base.

Despite being pushed out of Somalia's major cities and towns, al-Shabab continues to launch deadly guerrilla attacks across the Horn of Africa country. AU troops, government officials and foreigners are frequently targeted. The group has also carried out many deadly attacks inside Kenya.