MOGADISHU, Somalia (AP) — A roadside bomb killed a Ugandan peacekeeper in the Somali capital Friday, witnesses and an official said, breaking a brief period of relative quiet following a peace agreement between some of the fighting factions.

The explosion occurred near the Ugandan base at Mogadishu's international airport, said Ugandan commander Col. Godfrey Golooba.

Keyse Ali, a witness, said the bomb was hidden in a pile of garbage and exploded as the soldiers were making routine checks on the road. The blast knocked Ali back several yards.

Muhyadin Nor, another witness, said the area was covered in blood.

A spokesman for the African Union said the peacekeepers would continue their efforts.

"Unfortunately, this is not the first attack against our troops in Mogadishu," said El-Ghassim Wane at the AU's headquarters in Ethiopia. "But we are as determined as ever to carry out the mandate of the mission. ... This is an attack by elements bent on undermining peace efforts in Somalia."

African Union peacekeepers from Uganda and Burundi arrived in Somalia last year. The African Union force is separate from Ethiopian troops in the country, who are allies of the government and are not serving as peacekeepers.

The AU troops are mostly confined to bases near Mogadishu's airport, port and government buildings. The Ethiopians, who support the transitional government around the country, have suffered far heavier casualties.

In December 2006, the Ethiopian troops helped the government dislodge Islamists from power. The Islamists, who had taken control of the capital and much of the south, vowed to fight an Iraq-style insurgency.

But last month a more moderate faction signed a peace agreement with the government. The pact touched off a power struggle within the Islamist ranks, complicated by a web of clan loyalties.

Somalia has not had a functioning government since a group of clan warlords united to overthrow socialist dictator Mohamed Siad Barre in 1991, then turned their heavily armed militias on each other. The United Nations estimates half the population of the arid Horn of Africa nation will need food aid by the end of the year.

The aid group Doctors Without Borders said Friday that deteriorating stability might force it to stop sending its international experts to advise 800 local staff members there — or even disband operations entirely.

"We face increasing security threats in the country. We find it increasingly hard to do our work there, said Tankred Stoebe, the international organization's chairman in Germany, speaking in Berlin. "If it's going to get worse, we might be forced out of the country and have to leave the patients behind."

In January the aid group pulled out all of its 87 foreign employees from Somalia after three colleagues were killed there.

Associated Press Writers Anita Powell in Addis Ababa, Ethiopia, and Patrick McGroarty in Berlin contributed to this report.