Fighting between Somali warlords and Islamist militias for control of the capital, Mogadishu, has resumed for a sixth day after a brief lull.
The price of ammunition in the city has rocketed
Thousands have fled their homes, leaving the northern suburbs deserted and at least 130 people dead.
A hospital director in the city told the BBC that if the violence continued, medical supplies would run out.
The Islamists say the alliance of warlords are backed by the US, a belief fuelling the worst clashes in a decade.
The warlords accuse the Islamists of harbouring foreign militants.
The BBC's Mohammed Olad Hassan says the break in fighting on Friday morning gave both sides an opportunity to rearm.
The fighting is still concentrated in the CC district, where the clashes began on Sunday.
Both sides are vying for control of a strategic road leading out of Mogadishu.
Our reporter says there is a pattern: intensive shelling for long stretches followed by a few hours break in which only sporadic gunfire can be heard.
The price of ammunition has rocketed in the last week; a single AK47 round which cost 60 US cents last week now costs $1.50 on Mogadishu's open weapons market.
Dr Sheikh don Salad Elmi, the director of Medina hospital in South Mogadishu, where many have been brought in with severe injuries, said the fighting was affecting up to 200,000 inhabitants.
"We're afraid if the fighting goes on and the influx of wounded people increases in the hospital, we might not be able to cope," he told the BBC's World Today programme.
SOMALIA'S THREE RIVAL GROUPS
Gets arms from: Ethiopia, Italy (Source: UN report)
Gets arms from: Eritrea (Source: UN report)
Anti-terror alliance of warlords
Believed to get support from US
"The fighting has been intensive and is intensifying," he said
Most of those killed in the fighting are civilians caught in cross-fire or hit by stray bullets or shells, our reporter says.
"This is the first time we have witnessed people fighting in Somalia and targeting civilians in such a savage way," Mohamud Jama told the AP news agency at a hospital where he was tending his wife after a shell hit his home killing three of his children.
The US has not confirmed or denied backing the warlords but says it would "work with responsible individuals... in fighting terror".
A report by a UN committee on Wednesday warned that an unnamed country is flouting the arms embargo on Somalia.
The UN Security Council rejected the committee's recommendations for targeted sanctions and tighter controls on the illegal flow of weapons into Somalia.
This is the second round of Mogadishu's most serious fighting in a decade. In March, clashes between the two sides killed at least 90 people.
The militia linked to the Joint Islamic Courts have restored order to some parts of the city by providing justice under Sharia - Islamic law.
The alliance of warlords earlier this year created the Alliance for the Restoration of Peace and Counter-Terrorism.
It accuses the Islamic Courts of sheltering foreign al-Qaeda leaders, which they deny.
Last week, Somali President Abdullahi Yusuf accused the US of funding the coalition of warlords.
The US has an anti-terror task force based in nearby Djibouti.
Somalia has not had an effective national authority for 15 years since the ousting of President Siad Barre in 1991.