Somali insurgents threatened suicide attacks Thursday against African Union peacekeepers who are to be deployed in the coming days, as the capital's international airport came under mortar fire.

Gunmen shot dead two local officials in the capital, Mogadishu, which has been plagued by growing violence since the government, backed by soldiers from neighboring Ethiopia, drove out Islamists last year.

"No one was injured or killed," airport director Mohamed Ahmed Siyad told The Associated Press. At least two mortars exploded close to the runway but caused no damage, he said. The airport has been subjected to a number of mortar attacks.

Ethiopian troops stationed at the airport returned artillery fire, said eyewitness Falis Abdi Omar who was waiting to board a plane.

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.

Complete coverage is available in FOXNews.com's Africa Center.

"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 reading from a statement.

In Mogadishu the 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.

Government security forces arrested seven men overnight they accused of being terrorists, including Sheik Sharif Mohamed Ulusow, the imam of the country'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 African Union peacekeeping force, which is planned to reach a level of 8,000 troops, is meant to help the country's fragile, transitional government establish security in the country following decisive battles with a radical Islamic movement in December and January. The United Nations Security Council approved its deployment in a unanimous vote Tuesday.

"The Ugandan troops and those from the other African states who are being sent to Somalia are in our eyes no better than the Ethiopians who are occupying our country by force," said the extremist group's Web statement, which was signed by Harith Aba-Sadiq, who described himself as the "Organizer of Mogadishu People's Resistance."

Although insurgents have in the past threatened to attack any peacekeepers deployed in the country, this was the first time they have specified countries and the types of attacks they will launch.

The authenticity of the video, which echoes those released in Iraq and Afghanistan by Islamic insurgents, could not be independently verified. However, it is the second time this radical element allied to the Islamic movement has posted a video warning on the Internet.

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 its authority.

Get complete coverage in FOXNews.com's Africa Center.