Ethiopia fought a war against the Somali government in the late 1970s and early 80s, but there has been peace on the border for over a decade. So Ethiopia cannot point to internal safety concerns in allowing itself to be drawn into invading its neighbour.

The crisis has now escalated sharply with the deployment of US naval forces to prevent UIC fighters from fleeing, the US claiming that some have ties to terrorist organisations, including al-Qaida.

The Ethiopian invasion will certainly be resisted by Somali patriots. It will initially be classified as "successful" because it will establish a semblance of law and order. But the routed UIC, although weakened by internal squabbles, will seek safe havens nearby, regroup and woo back its supporters.

The UIC knows that when faced with a conventional army backed by an airforce, the best option is to disappear into the undergrowth or behind the desert dunes. The Somalis have been "disappearing" like that for centuries, always coming back to harass those who claim to have defeated them.

The danger this time is that the resistance will draw in other countries. Eritrea, which fought its own costly war with Ethiopia, does not need an invitation to help its enemy's enemy. The UIC is also said to be receiving financial assistance from rich leaders of sympathetic Islamic sects, drawn from such countries as Saudi Arabia, Yemen and the Gulf sheikhdoms. And the most explosive fuel will be the involvement of the US on the side of Ethiopia. General John Abizaid, commander for the US central command, is reported to have visited Ethiopia last month, after which Ethiopia moved from providing the Somali government with "military advice" to open armed intervention.

The US objective is to safeguard access to the Red Sea for its oil tankers, and to prevent al-Qaida cells being nurtured in Somalia or in Ethiopia, which has a sizeable Muslim minority. Now, by allowing the US to persuade it to invade, Ethiopia has signalled to the Islamic world that it is willing to join the US in its "war on terror".

Can Ethiopia afford to be universally regarded as a US puppet? In the African Union (AU) - which has its headquarters in the Ethiopian capital, Addis Ababa - US policy is already causing enormous confusion. For months the AU has been trying, unsuccessfully, to persuade the UN security council to bolster the AU force in Darfur, Sudan. Yet within days of Ethiopia's invasion, the security council, under US instigation, was able to pass a resolution asking for an AU force to be sent to Somalia. Clearly, the US wants to legitimise the invasion by placing it under the umbrella of the very AU that it has humiliated for months.

As one of the poorest countries on earth, Ethiopia needs to have the solidarity of the "wretched of the earth". In allowing itself to be associated with George Bush's foreign policy, it is placing itself on the wrong side of the struggle between the weak and the strong.

- Cameron Duodu is a Ghanaian novelist and journalist duodu@homechoice.co.uk

Abdirahman Dinari, a spokes-man for Somalia's transitional federal government, said the Islamists "were being surrounded from every direction" in the district of Badade. "The fighting is going on. We hope they will either surrender or be killed by our troops. Their resistance is failing. Some of them are trying to escape by sea, but US anti-terrorist forces have been deployed there to prevent them." In Washington, a State Department spokesman, Sean McCormack, said US Navy vessels were looking for al-Qa'ida members and their allies.

The US, which claims attacks on its embassies in East Africa had been organised by al-Qa'ida members based in Somalia, also has personnel working with the Kenyans at the border.

The Kenyan Foreign Affairs minister, Raphael Tuju, said: "We will not allow combatants and their families to use this country as a base. It is apparent that some so-called refugees are combatants on the run. We have arrested men holding British, Canadian, Eritrean and Danish passports."

But the United Nations said an acute humanitarian crisis was developing in the wake of the fighting, with almost 10,000 Somalis encamped at the town of Doble, near the Kenyan border. Geoff Wordley, of UNHCR, said: "The situation is pretty bad, these people have no assistance, or food or water." The US Secretary of State Condoleezza Rice, said the US will provide $16m (£8.1m) in aid to Somalia. Of this $11.5m will be in food, $1.5m in non-food assistance and $3.5m to help refugees.

Jendayi Frazer, the assistant US secretary of state for Africa, said there had been no request for US troops or military assistance for an airlift, but that she did not rule out that it could be requested and supplied later if necessary. In Somalia, the Interior Minister, Hussein Aideed, claimed that "there are 3,500 Islamists hiding in Mogadishu and they are likely to destabilise the security of the city".

Mr Aideed, son of the warlord the Americans attempted to capture or kill during their ill-fated intervention in Somalia, portrayed in the film Black Hawk Down, is now a staunch ally of Washington. He added that the Islamists may begin the bombing campaign they had threatened since being driven out of the Somali capital by Ethiopian and government forces.

But a fresh outbreak of violence in Mogadishu appeared to be the responsibility of warlord-led militias who had reoccupied the city since the demise of the Islamists.

Militia fighters were accused of opening fire at an oil tanker in the outskirts of the city. The driver, Ali Tusbah, said afterwards: "The militias fired three RPGs [rocket-propelled grenades] at us and one of them hit my truck. They were bandits who wanted money, just like the old days."

The Somali government, which could barely control the one remaining city, Baidoa, under its jurisdiction, has given Mogadishu residents three days to hand in weapons.

Mr Aideed said: "It can, in fact take years. The three days should not be taken literally. Disarming Somalis is not easy. The government will have a tough time collecting the arms and specifically the small-arms."

Very few have been handed in. One resident said: "I have an AK-47 and a pistol. I will not surrender them because I don't see any trustworthy person to give them to. People have started burying their weapons. Others have transported their heavy weapons outside Mogadishu."

The Ethiopian Prime Minister, Meles Zenawi, said he wanted to withdraw his troops within a few weeks. Talks are being held for an African Union force to replace them.