Hundreds of people have taken to the streets of the Somali capital Mogadishu in protest at the presence of Ethiopian forces backing the interim government.
Many Somalis want the Ethiopians to go
Witnesses said security forces fired in the air to disperse crowds, as youths burnt tyres and threw stones.
At least one civilian was killed and several others injured by gunfire, but it was not clear who was responsible.
The protests came as the government indefinitely postponed a forcible disarmament programme in the capital.
Elders of the biggest clan in Mogadishu complained that the programme was one-sided and did not apply outside the capital.
The original deadline for handing in weapons was Thursday but few people have done so.
Observers say Mogadishu is awash with weapons, and violence has increased since Ethiopian-led troops ousted Islamist militias.
A 13-year-old boy was killed when government forces opened fire on demonstrators, his family told AFP news agency.
SOMALIA IN NUMBERS
Ethiopia troops: 8,000-15,000
Government troops: 10,000
Islamists: 600 near Kenyan border; 3,500 around Mogadishu
Recently displaced: 30,000
Refugees in Kenya: 160,000
Sources: Somali government, UN, correspondents
"Some government troops and Ethiopian forces opened fire to disperse the crowds and my son was hit by a bullet," Omar Halame Rage told AFP.
"This is unacceptable and an inhuman action. We don't need those Ethiopian forces with their government soldiers if they are shooting our children," he is quoted as saying.
The Somali police said protesters threw stones at government forces, provoking the shooting that they said was an act of self defence.
Saturday's riots are the third to hit Mogadishu since Ethiopian and Somali troops arrived on 28 December, ousting Islamist forces that had taken control in June.
The Islamists have vowed to wage a guerrilla war against the Ethiopians. Al-Qaeda number two Ayman al-Zawahiri has reportedly urged the Islamist militias to fight the "crusaders".
"I call upon the Muslim nation in Somalia to remain in the new battlefield that is one of the crusader battlefields that are being launched by America and its allies and the United Nations against Islam and Muslims," a five-minute tape, posted on a website used by militants, said.
On Friday, Somali interim President Abdullahi Yusuf called for a "speedy deployment" of the AU force, agreed by the UN Security Council before the current hostilities.
Speaking at a Nairobi meeting, he said there was a rare chance for a real political breakthrough in Somalia, plagued by violence for 15 years.
The US has agreed to provide $10m (£5.2m) towards the funding of the 8,000-strong peacekeeping force - part of $40m pledged to support Somalia's efforts to restore stability.
Ethiopia's Prime Minister, Meles Zenawi, has said he wants his forces out of the country in a matter of weeks.
Kenya's government has shut its border with Somalia, despite criticism from the United Nations' refugee agency.