Somali government forces, supported by Ethiopian soldiers, entered Mogadishu unopposed today after the leaders of Islamist militias that have controlled the city since June fled last night.

"We are in Mogadishu," said Mohamed Ali Gedi, the Prime Minister of Somalia's interim Government, after talks with the clan elders who are the ultimate powerbrokers in the ravaged capital. "We are coordinating our forces to take control of Mogadishu."

A spokesman for the interim Government said that Somali soldiers backed by Ethiopian tanks and aircraft started moving into the outskirts of the city after seizing the main roads in Mogadishu early today.

The official, who spoke on condition of anonymity, said that the Government had abandoned its plan for a siege and decided to take Mogadishu after being told that the leaders of the Union of Islamic Courts (UIC) had left their base and that armed clans were beginning to loot the city, which has around 2 million inhabitants.

"People were crying for the Government to come as early as possible so we changed our plan," said the spokesman. "The Government is now calming the situation and telling the militias to go to camps to avoid clashes. The Government is being welcomed."

The Prime Minister of Ethiopia, whose military support has enabled Somalia's official, but weak, government to roll back the Islamist militias that have taken over much of the country since gaining control of Mogadishu six months ago, said the capture of the capital would lead to the final defeat of the Islamists "in days, if not in a few weeks".

"We are discussing what we need to do to make sure Mogadishu does not descend into chaos. We will not let Mogadishu burn," said Meles Zenawi in Addis Ababa.

But the leaders of the courts movement, which had brought a semblance of order to Somalia's anarchic capital through the strict application of Islamic law, described their withdrawal from Mogadishu as tactical and an attempt to spare the lives of civilians caught up in the conflict, which burst into outright war on Saturday.

"We want to face our enemy and their stooges... away from civilians," Abdirahman Janaqow, an Islamist militia leader, told the Associated Press.

Fighters loyal to the UIC, which has suffered a series of defeats at the hands of the better-equipped and better-armed Ethiopian forces, were reported to be gathering in Kismayo, a southern town still controlled by the Islamists. Residents also reported Islamist troops with pickup trucks and mounted machine guns recruiting children as young as 12 to join their militias in Jilib.

While many Islamist militias are thought likely to lay down their arms, around 3,000 hardliners, including young, foreign-trained fundamentalists are expected to continue fighting and could launch a prolonged guerrilla war.

Some leaders have also threatened to send suicide bombers to Addis Ababa, the capital of mainly-Christian Ethiopia, while a statement purportedly from al Qaeda in Iraq was posted on a militants' website last night, asking fellow extremists to support their Somali counterparts with "weapons and men and with prayers".

In Mogadishu, residents anxiously waited to see whether interim Government could negotiate a sturdy settlement with the clan elders who control the capital's rampant gunmen and gangs. The withdrawal of the hardline Islamists has raised fears that the city could slip back into the endemic factional fighting of the last decade.

"Uncertainty hangs in the air," Muktar Abdi, a Mogadishu resident, told Reuters. "My worst fear is the capital will succumb to its old anarchy. The Government should come in now and take over — this is the best chance they have before the city falls into the hands of the warlords again."

President Abdullahi Yusuf, the leader of the interim Government, released a statement seeking to assure the people of Mogadishu, saying: "We are tirelessly working toward the salvation or our nation and the restoration of your dignity and honor."

Somalia's UN-backed interim Government — the 14th attempt to restore central rule since the fall of the Siad Barre, the military dictator, in 1991 — has managed to turn the tide against the Islamist militias largely because of the military support of Ethiopia, the country's traditional enemy and one of the best-armed nations in the region.

The Ethiopian Government has justified its intervention by arguing that the Islamist militias were threatening to provide a base for al-Qaeda in the Horn of Africa and were lending support to Eritrea, its other rival. But its presence within Somalia has caused consternation, with the Arab League and Qatar, the only Arab representative on the UN Security Council, demanding its withdrawal as a precondition for any ceasefire.