Much of Somalia's capital has become a ghost town as more than 200,000 residents have fled intensified clashes between Islamist insurgents and government troops, the U.N. and a medical charity said Tuesday.

Doctors Without Borders announced it had been forced to close a pediatric hospital and three health clinics in the north of Mogadishu — the first time it has done so for 17 years.

The organization is one of the few charities remaining in the country.

The charity has struggled to deliver health care to hundreds of thousands of desperate Somalis, continuing to operate even after staff have been kidnapped or killed.

No one knows how many remain trapped between Mogadishu's shifting front-lines since clashes intensified in May and no precise casualty figures for the latest fighting are available. The U.N. refugee agency says 204,000 Somalis have fled Mogadishu since May.

The northern suburbs are virtually deserted apart from fighters who have taken over buildings that include medical facilities, the charity said. Mogadishu was believed to have 2 million residents in 2007, but up to half that number have since fled.

Residents usually leave at dawn, seeking a lull between the fighting. Those who can't afford overloaded minibuses set off down the streets on foot, possessions on their heads and babies in blankets slung over their fronts and backs.

Some Somalis have moved several times. Families face an agonizing choice: stay in streets where men fire mortars and machine-guns that have killed children asleep in their beds, or head out of town, where camps for the displaced are severely overstretched.

MSF said half a million people are already camping along the main road that links Mogadishu to the nearby town of Afgoye. Most are sleeping outside under plastic strung over twigs. It is freezing at night and sweltering by day. There is very little food or water. Attacks are common.

Insurgents have been battling the government since an Islamist administration was overthrown in 2006. The latest round of fighting began when an exiled Islamist leader returned to the country to challenge the new president, a former ally elected by Parliament in January. It had been hoped the election of Sheik Sharif Sheik Ahmed would help undercut support for the Islamists, but instead the often-competing insurgent factions have temporarily coalesced and have seized much of the capital.

The Horn of Africa nation has not had a functioning government for 18 years since clan warlords overthrew a brutal socialist dictator then unleashed their militias on each other.