"Protesters shot at policemen, the police returned fire killing one man," a government source told Reuters news agency.
"I don't know how many people have been wounded."
Relatives of the 13-year-old boy blamed the Somali government and Ethiopian soldiers for his death.
"My son was from school. He was going with some people who were demonstrating. Some government troops and Ethiopian forces opened fire to disperse the crowds and my son was hit by a bullet," the boy's father told AFP news agency.
"They shot him in the back and the bullet shattered his heart. 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 added.
Ethiopian soldiers entered the country in support of the weak interim government to fight the Union of Islamic Courts which had gained control of much of the country.
The courts were beaten within two weeks, with some fighters melting into the civilian populace and others trying to flee to Kenya.Anti-Ethiopian protest
The protest was the third to hit the capital since the government and the Ethiopian forces moved into Mogadishu.
Hundreds of Somalis had marched through the streets of the capital chanting "Down with Ethiopia".
|"We have not given a specific time, but in the near future the disarmament will be done all over the country."|
Ali Salad Jelle,
Somali deputy defence minister
The government had demanded that Somalis give up their arms by Thursday but on Saturday they abandoned the programme after few people came forward to willingly hand over their weapons.
Ali Salad Jelle, the deputy defence minister, said the disarmament had been postponed indefinitely after members of the Hawiye clan, the majority clan in the capital, asked the prime minister to stop it.
Dahail Abukar, a protester, said: "We don't want disarmament only in Mogadishu, we want all the people [of Somalia] and all the clans to be disarmed simultaneously."
Mohammed Adow, Al Jazeera's correspondent in Mogadishu said: "They [the protesters] are looking at the disarmament issue from a clan basis and arguing that they will be unable to defend themselves if they hand in their weapons."
The protests come just days after an ambush killed one Ethiopian soldier in south Somalia, and a hand grenade was thrown at Ethiopian troops in Mogadishu.
The Somali capital is flooded with small arms. The ease with which Somalis can get weapons is a major problem, and only a few were seen to be disarming under Gedi's disarmament programme.
The US has pledged to provide $40mn to Somalia in political, humanitarian and peacekeeping assistance.
|Protesters in the capital shouted: |
"Down with Ethiopia"
The package will include a plan to ask more African nations to provide troops to help stabilise the country.
The EU said it would help pay for a peacekeeping force envisioned at 8,000 soldiers.
US warships have patrolled the Somali coast to prevent Islamic Courts fighters from escaping by sea.
Ethiopia's government has said that it does not intend to stay in Somalia for long, saying its forces cannot be peacekeepers and it cannot afford for them to stay.
More than 3,000 Islamic Courts fighters are allegedly still hiding in the capital.
Kenya closed its border with Somalia amid fears that Islamic Courts fighters would slip across the frontier. The UN said thousands of refugees were also near the border, unable to seek safety in Kenya.
The UN office for the co-ordination of humanitarian affairs (Ocha) said in a statement on Friday that fighters were reported to be on the roads to towns in southern Somalia looting and harassing civilians.
Ocha said that Ethiopian soldiers have also detained a UN security staff member in one southern town and his whereabouts are unknown.
A tape, believed to be from al-Qaeda's deputy leader, has urged defeated Courts fighters to launch an Iraq-style war against Ethiopian forces there.
"You must ambush, mine, raid and [carry out] martyrdom campaigns so that you can wipe them out," he said.
The message is likely to reinforce Washington's belief that the Council of Islamic Courts is linked to al-Qaeda, a charge that the Islamic Courts have denied.
The audiotape could not be independently verified.