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.

Kenya vowed Saturday to keep troops in Somalia as long as needed to prevent attacks on its soil by the Islamist group Shebab and called for reinforcements in an increasingly regionalized conflict.

"When the Kenyan government and the people of this country feel they are safe enough we shall pull back," the country's military chief General Julius Karangi told journalists Saturday, refusing to put a timeline on the operation.

Fighters from Somalia's Shebab Islamist group attacked a government military base in Mogadishu Saturday, where a blast was followed by an exchange of gunfire, officials and witnesses said.

Enemy "elements attacked a Somali military base near the industrial road (north of the city center), but they were defeated and suffered losses", Colonel Abdallah Mohamed of the Western-backed government forces told Agence France Presse.

A Kenyan man was sentenced to life imprisonment Friday after he admitted involvement in a grenade attack and membership of the al-Qaida linked Somali Shebab militant group.

"This sentence is harsh because police have provided evidence showing he intended to hurt the public," said Judge Grace Macharia at the sentencing of Elgiva Bwire Oliacha. "It is also meant to be a deterrent," she added.

Attackers fired a rocket-propelled grenade at a vehicle and killed four people in northern Kenya Thursday, police said.

"The vehicle was carrying eight people but four of them have died," a police officer in the region said on condition of anonymity.

Grenade blasts at a blue-collar bar and a crowded bus stop rattled Nairobi, as the country worried whether al-Qaida-linked militants from Somalia were carrying out their promise to launch reprisal attacks in Kenya's capital.

The attacks on Monday came only two days after the U.S. warned of "imminent" terror attacks.

A grenade was thrown into a discotheque in the Kenyan capital Nairobi early Monday injuring 14 people, all Kenyans, in an attack police linked with recent threats made by Somali Shebab insurgents.

"Yes, we are linking the grenade attack to the threats that have been issued by Shebab and that is why I am appealing to city residents to be vigilant and cooperate with our officers," Antony Kibuchi, provincial police chief for Nairobi, said.

The Somali kidnappers of a disabled Frenchwoman who died after being snatched from her home in Kenya are demanding a ransom for the return of her body, France said on Thursday.

"The hostage-takers are even trying to sell the remains, it could not be more despicable," French Defense Minister Gerard Longuet told the i-TELE news network.

African Union and Somali government troops battled Shebab rebels in the anarchic capital Mogadishu Thursday, as Kenyan troops in the south continued their assault on Islamist positions there.

Heavy fighting broke out before dawn in Mogadishu as AU-backed Somali forces advanced on holdout Islamist Shebab positions, officials and witnesses said.

Kenyan jets struck Shebab positions in Somalia Wednesday in a bid to rid the border area of Islamist rebels they blame for a spate of abductions, including that of a French woman who died in captivity.

Kenyan ground troops guided by pro-government Somali forces prepared for a fresh assault against the insurgents with the blessing of the Western-backed government in Mogadishu and its Ugandan protectors.