NAIROBI - Somali Islamists are under the growing control of an al Qaeda cell in East Africa, a US diplomat said on Thursday, as Washington condemned their threat to attack Ethiopian troops backing Somalia's interim government.

Somali Islamist fighters disembark from a 'technical' vehicle in Mogadishu's Tarbuunka square, November 28, 2006. [Reuters]

"The Council of Islamic Courts is now controlled by al Qaeda cell individuals, East Africa al Qaeda cell individuals. The top layer of the court are extremists. They are terrorists," US Assistant Secretary of State Jendayi Frazer told reporters.

"They are killing nuns, they have killed children and they are calling for a jihad (holy war)," she added.

The Islamists, who seized the Somali capital Mogadishu in June and are vying with the weak transitional government for control of the lawless country, have denied having foreign fighters in their ranks.

The defense chief for the Mogadishu-based Islamists on Tuesday issued a threat to attack Ethiopian troops backing Somalia's interim government unless they leave within days.

He said Ethiopia had sent more than 30,000 troops to bolster the Somali government in Baidoa, the only town it controls in the country.

Addis Ababa said it only had a few hundred trainers with the Somali government, which is backed by the West in a 14th attempt since 1991 to restore central rule to the conflict-riven nation.

U.S. Embassy spokeswoman Jennifer Barnes said from Washington's Nairobi mission, responsible for Kenya and Somalia: "The United States regrets the irresponsible 'ultimatum' issued by the Islamic Courts.

"Given the existing heightened tensions in Somalia, this ultimatum further destabilizes the situation and undermines international and regional efforts to encourage credible dialogue between Somali parties."

The Islamists' December 19 deadline for Ethiopian withdrawal has heightened fears of all-out war in Somalia, where skirmishes have taken place between reconnaissance teams from government and Islamist troops close to each other near Baidoa.

A senior leader of the Somalia Islamic Courts Council (SICC) said in Yemen it would only hold talks with Ethiopia when Addis Ababa withdrew its troops.

"Otherwise their fate will be defeat and we will fight them until we evict them from Somalia," Sheikh Sharif Ahmed told the state-owned Yemeni satellite channel from Aden.

Since taking Mogadishu, the Islamists have expanded across south Somalia.

Washington believes at least three of the plotters behind the 1998 U.S. Embassy bombings in Tanzania and Kenya are in Somalia. The head of the Council of the Islamic Courts, Sheikh Hassan Dahir Aweys, is on U.N. and U.S. terrorist lists.

WAR INEVITABLE?

Fighters from the religious movement effectively flank the government on three sides, and rival soldiers are just a few kilometers apart at a slim front line near Baidoa.

"If the so-called Islamic Courts and their alliances are determined to spark war in Somalia then it is inevitable to happen -- but the government is ready to defend," Somali Prime Minister Ali Mohamed Gedi told reporters in Nairobi.

Diplomats fear any fighting could spill into a regional war as Ethiopia openly supports the government while its arch foe Eritrea is accused of sending arms and fighters to help the Islamic Courts.

Foreign nations are urging the Somali rivals to return to peace talks, which stalled in Khartoum last month.

However a U.N. resolution endorsing an African peacekeeping mission -- which the government wants, but the Islamists have sworn to fight -- has made a quick resumption of talks unlikely.

Despite its own disastrous intervention in Somalia in the 1990s -- depicted in the Hollywood film "Black Hawk Down"" -- Washington argues the arrival of a formal African peacekeeping force to protect the government would pave the way for an exit of Ethiopian and Eritrean forces in Somalia.

African Union Commission Chairman Alpha Omar Konare backed that view at a regional summit in Kenya. "If we do not do this now, then we must prepare ourselves for the emergence of ethnic republics and religious republics in the coming years," he said.

Eritrea called for a special meeting of east African inter-governmental body IGAD to discuss the resolution.