At least 16 people have been killed and 56 injured in the Somali capital Mogadishu, during a shoot-out between troops and police.
The BBC's Mwalimu Mohamed in Mogadishu said the incident was sparked when a soldier shot dead a policeman near Benadir hospital.
When police arrived at the scene, the two sides - who both support the UN-backed government - exchanged fire.
Somalia has not had a functioning national government for 20 years.
Most of those killed were reported to be civilians who had been shopping in the crowded Benadir market.
The clash was ended when other troops intervened.
Defence Minister Abdihakin Mohamed Fiqi visited the Madina hospital to express regret over the deaths.
"On behalf of the Somali government, the president, his prime minister and the speaker, we are very sorry about the sad incident," the AFP news agency quoted him as saying.
"We will help the wounded and promise to bring those behind the brutal killing to justice," he said.
Our correspondent says it is not the first time that the armed forces have opened fire after a dispute and that residents of the capital have often complained about their indiscriminate firing.
Such clashes are an indication of lack of discipline and command in the country's security apparatus after 20 years of civil war, he adds.
The government is battling the al-Qaeda-linked al-Shabab movement for control of Mogadishu.
Al-Shabab and other Islamist groups control most of southern and central Somalia. BBC News
