Scores of residents were killed over the weekend and hundreds more trapped in their homes as the worst fighting in 15 years battered the ruined Somali capital, Mogadishu.

Allied Ethiopian and Somali government troops fired tank and mortar rounds into heavily populated areas for the fourth day running, in an attempt to flush out insurgents backed by remnants of Islamists driven from power in December.

The International Committee of the Red Cross expressed deep concern for thousands of civilians trapped by the fighting which it said was the worst seen since the early 1990s when militias fought with US special forces hunting wanted Somali warlords.

An outraged Somali working for the United Nations accused the Ethiopians, who have used tanks and helicopter gunships to pound rebel positions, of committing “war crimes”.

“They are firing heavy artillery into residential areas . . . innocent people who have nothing to do with these insurgents, let alone Islamists, are being slaughtered. Where are all those human rights groups who go on about Mugabe now; this is ethnic cleansing dressed up as a war on terror,” he told The Times.

Estimates of the number of people killed vary widely. Some now put the death toll as high as 150, but with most of the Indian Ocean port city a “no-go” area it is impossible to verify. Hospitals across the city are overflowing with wounded. Residents say that they represent only a fraction of the casualties.

Some of the heaviest fighting has taken place in the Ali Kamin neighbourhood, a rabbit warren of narrow alleyways, and the area around the main stadium in south Mogadishu, for years a stronghold of Somali gunmen.

Witnesses said yesterday that they saw at least six bodies of civilians lying in the street, unable to be retrieved by relatives because of heavy crossfire.

“There are tanks everywhere. Shells are landing everywhere and this is very scary,” Hussein Ali, a resident said. “I cannot confirm the exact casualties, but a lot of people have been killed and others wounded.”

Witnesses also reported the charred bodies of Ethiopian soldiers, near a burnt out army truck, and said that tanks had taken up position on main crossroads. All access to the areas of the heaviest fighting have been prevented by road-blocks manned by a joint force of Ethiopian and Somali government forces.

In another ominous development, a Ugandan peacekeeper – part of an African Union (AU) force supposed to maintain order after an Ethiopian Army pull-out – was killed on Saturday and five others wounded after mortars fired by the insurgents slammed into their base at the Presidential Palace. “We are not surprised by what took place, we expect those people [insurgents] to do more of such things. We are not in any fear at all,” Major Fe-lix Kulayigye told journalists in the Ugandan capital, Kampala.

Regional experts, however, said that the AU force, which controls the airport from where the Ethiopians had launched helicopter raids against suspected insurgent positions, was no longer seen as a neutral force.

The US, which has supported the Ethiopian incursion, says that the Islamists have links to al-Qaeda. Somali experts say there are some links, but the imposition of a President from the Darod clan of southern Somalia has united rivals in the Hawiye sub-clans of central Somalia against a common foe.

“This is clan-based civil war now, the Islamists are fighting on the side of some of the Mogadishu clans but they are not leading this insurgency. It is very dangerous for the AU forces,” said a Somali expert. He cannot be identified for fear of reprisals in neighbouring Kenya to where many Somalis have fled.

The Ethiopians drove the Islamists from power in December, ending the only period of calm the city has seen since 1991, when Mohammed Siad Barre, the former Cold War dictator, was overthrown.

Times Recommends

• Tehran cannot live up to its rhetoric
• The new unicycle that will ‘change the world’
• We cannot wish away Iran’s bomb