MOGADISHU — An American citizen of Somali origin was one of the two suicide bombers behind a twin attack on a pro-government military base in Mogadishu, the Islamist Shebab movement said on Sunday.

Several pro-Shebab radio stations broadcast what they said were the last words of Abdusalam al-Muhajir who said that he "wanted to die as a martyr" after spending the last two years fighting alongside the rebels.

"I am an American citizen who grew up in the United States after my parents took me there at the age of two," he said in the message which was broadcast a day after the attack on an African Union base in the capital.

Sheikh Mohamed Ibrahim, a Shebab spokesman, told AFP that "two young and brave mujahideen warriors, one who came from the United States, led the holy attack that killed many enemies yesterday."

The African Union peacekeeping force (AMISOM) in Mogadishu issued a statement after the attack, saying its troops had "beaten off an attack by Al-Qaeda linked terrorists on one of their positions in the outskirts of the city.

AMISOM spokesman Paddy Ankunda said that two of its soldiers had been wounded in the attack.

In their statement issued on Saturday, the Shebab claimed to have killed 80 Ugandan soldiers in a battle that lasted over two hours.

Uganda and Burundi provide the 9,000 soldiers that currently comprise the AU mission in Somalia, which is tasked with defending the fragile interim government from the insurgents.

The Shebab, who control large swathes of territory in south and central Somalia, withdrew from their positions in Mogashishu in early August following a government offensive launched in February.

They have claimed credit for a series of bombings since, including an October 4 blast at a government complex that killed 82, the deadliest single attack ever committed in Mogadishu.

Apart from the African Union troops, Kenya sent an undisclosed number of troops into southern Somalia two weeks ago in an operation against the Shebab whom it blames for a spate of kidnappings of foreigners on Kenyan soil.

Dozens of young US citizens, most of them of Somali origin, have left their homeland in the last four years to join up with the Shebab, according to the US department of justice.

Several of those recruits have died in the fighting, including a man identified by the Shebab as Dahir Gurey Cheikh Ali Guled after he was killed in September last year.

Tens of thousands of Somali immigrants and their American-born children live in the United States, many of them clustered in the twin cities of Minneapolis-St. Paul, in the midwestern state of Minnesota.