MOGADISHU, Somalia - Extremists in Somalia threatened to carry out suicide attacks against African Union peacekeepers who are to begin deploying in the coming days, and the capital's international airport came under mortar fire Thursday.

At least two mortar rounds exploded near the runway but caused no damage, airport director Mohamed Ahmed Siyad told The Associated Press. There were no injuries, he said.

Ethiopian troops stationed at the airport returned fire, said Falis Abdi Omar, who was waiting to board a plane at the airport, which has been the target of a number of mortar attacks.

In the capital, Mogadishu, two local government officials were gunned down late Wednesday. One was killed as he returned from a mosque where he had been praying. No one has claimed responsibility, although two suspects have been arrested, said the country's deputy defense minister.

Meanwhile, a newly formed extremist group known as the Popular Resistance Movement in the Land of the Two Migrations posted a new warning against planned peacekeepers.

"We promise we shall welcome them with bullets from heavy guns, exploding cars and young men eager to carry out martyrdom operations against these colonial forces," said a man who appeared in a video posting on an Islamic Web site. He was reading from a statement by a newly formed extremist group known as the Popular Resistance Movement in the Land of the Two Migrations.

Government security forces also arrested seven men overnight they accused of being terrorists, including Sheik Sharif Mohamed Ulusow, the imam of Somalia's largest mosque, which draws crowds of up to 40,000 people at times of worship.

Hundreds of families have begun fleeing Mogadishu, a coastal city of 2 million people, and hospitals say they are struggling to cope with the daily influx of wounded.

The AU force's first troops, a small Burundian advance team, are scheduled to be on the ground as early as Friday. Uganda canceled a Wednesday news conference without explanation at which it planned to announce a date for deployment of its force.

The peacekeepers will have to confront the growing violence that has plagued Mogadishu since the government, backed by soldiers from neighboring Ethiopia, drove out an Islamic group that had ruled the capital and most of the south of Somalia.

Since then, insurgents have staged near-daily attacks, with Mogadishu's civilian population bearing the brunt of the violence.

Ethiopian troops, largely seen as an occupying Christian force, have been accused of indiscriminate attacks against civilian-populated areas.

Uganda said Thursday the new threats from the extremist group would not prevent its own deployment. The country is preparing to send 1,500 troops to Somalia.

"We are sending seasoned fighters who have been dealing with our own insurgency," said Major Felix Kulayigye. "Our troops have been fully trained and are prepared for suicide bombers."

He added that no date had been fixed for their deployment.

The AU peacekeeping force, which is planned to reach a level of 8,000 troops, is meant to help the fragile, transitional government establish security in the country following decisive battles with a radical Islamic movement in December and January. The U.N. Security Council approved its deployment in a unanimous vote Tuesday.

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.

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