Updated

Somalia's interim government began imposing martial law in areas under its control, the prime minister said, as rising violence threatens its tenuous grip on power.

A curfew was imposed Tuesday night on the southern Somalia town of Baidoa, as Prime Minister Ali Mohamed Gedi warned remnants of an ousted Islamic movement have returned to the towns and cities and are planning to destabilize the lawless country.

"From now on the martial law would be implemented across government controlled areas, starting with Baidoa tonight," Gedi told government-controlled radio late Tuesday.

The three-month long emergency law was announced on Jan. 13 but was never implemented. Its imposition came as African leaders meeting in neighboring Ethiopia failed to make up a shortfall of 4,000 troops for a peacekeeping mission to Somalia.

Fears are mounting that Somalia could again be plunged into civil war without a peacekeeping force. Since the Islamic movement was ousted by Somali government troops backed by Ethiopian soldiers, tanks and war planes, factional violence has again become a feature of life in the Somali capital, Mogadishu.

Ethiopia has begun withdrawing its forces, and diplomats are warning it could create a power vacuum that Islamic fighters could take advantage of.

On Tuesday night, unknown gunmen attacked Ethiopian bases on the northeastern outskirts of the capital with rocket propelled grenades. There was no word on casualties among soldiers. A witness said that no civilians were hurt.

Extremists in Somalia warned Tuesday that they would try to kill any peacekeepers deployed to the war-ravaged country.

In a videotape posted on the official Web site of Somalia's routed Islamic movement, a hooded gunman read a statement saying that any African peacekeepers would be seen as invaders.

So far five nations — Uganda, Nigeria, Malawi, Burundi and Ghana — have pledged around 4,000 troops.

"Somalia is not a place where you will earn a salary — it is a place where you will die," one militant, carrying an assault rifle and dressed in military fatigues, said in the warning to the peacekeepers. "The salary you are seeking will be used to transport your bodies."

Five other hooded gunmen were visible in the video, armed with machine guns and rocket-propelled grenades.

The top U.S. diplomat for Africa, Jendayi Frazer, told reporters at the African Union summit where the peacekeeping force was being discussed that "we will not be intimidated."

The U.S. has accused the Islamic group of sheltering suspects in the 1998 Al Qaeda bombings of U.S. embassies in Kenya and Tanzania. Usama Bin Laden has said Somalia is a battleground in his war on the West. The U.S. launched at least two airstrikes against fleeing Islamic fighters, although details of the attacks are unknown.

Somalia has not had an effective national government since 1991, when warlords overthrew dictator Mohammed Siad Barre and then turned on one another, throwing the country into anarchy.

A transitional government was formed in 2004 with U.N. help in hopes of restoring order, but it has struggled to assert authority.