This high-tech, covert battle is part of a broader US effort against suspected terrorists. It surfaces only rarely, with news of a sudden air strike that has killed a Taliban commander in Afghanistan, or an al-Qaeda operative in Yemen.

Last week the US and its allies claimed a devastating blow against a force of some 150 insurgents who had been monitored as they gathered in Pakistan, and were attacked as soon as they crossed into eastern Afghanistan.

But the most overt example of this hidden conflict came late on Monday, with the first report that US forces based at Camp Le Monier had launched at least one deadly strike against suspected Islamist extremists in neighbouring Somalia. The attack - involving a bullet-belching AC-130 gunship - was aimed at al-Qaeda suspects accused of carrying out the 1998 bombings of two US embassies in east Africa. The US admitted its operation failed: though officials said "five to 10" militants were killed, no high-value targets were among them. Other independent reports said dozens of innocent civilians had died in a series of air strikes.

The attack threw into fresh focus the chaotic situation in Somalia. Ethiopian forces, backed by the US, were behind a recent offensive that ousted an Islamist government known as the Islamic Courts, and reinstalled a weak government headed by prime minister Ali Mohamed Gedi.

But more pertinently, the strike by the US close to the Kenyan border last Sunday - using an aircraft equipped with cannons, a howitzer and heavy machine guns - is one of just a handful of operations carried out from Camp Le Monier that the US, and the Combined Joint Task ForceHorn of Africa, has made public. "It's known as a secret war for a reason, " said John Pike, a military analyst with GlobalSecurity. org, based in Washington.

Of the base, which the US recently signed a lease with the Djibouti authorities to expand from 80 to 800 acres, he added: "It's located in a part of the world where you'd want to know if foreign fighters are suddenly arriving. I imagine they are developing informants all over the place, probably through intermediaries."

A previous insight into the sort of operations launched out of Djibouti came in November 2002, when the US dispatched an unmanned Predator drone, equipped with Hellfire missiles, from Le Monier to silently hunt down an alQaeda suspect, Qaed Salim Sinan al-Harethi.

Tracked through an intercepted mobile phone call, he was driving through the deserts of southern Yemen when a missile killed him and five colleagues, leaving nothing but a pile of debris smouldering in the sand 100 miles east of the capital, Sana'a.

Following that attack it was speculated that the drone had been "flown" - physically operated using a joystick - from hundreds or even thousands of miles away, either in Le Monier or at CIA headquarters at Langley, Virginia. The $30,000, 27ft drone, flying at 25,000 feet, was equipped with a real-time camera and a laser. Harethi and his friends probably never knew they were being targeted.

More recently, Mullah Akhtar Mohammad Osmani, described as one of the Taliban's most senior leaders and said to have close links to Osama bin Laden, was killed by a remarkably similar air strike in Afghanistan. The Taliban commander's car was destroyed last month on an isolated desert road in southern Helmand province, where British forces are engaged in regular fighting. It emerged that Osmani had also been tracked through his mobile or satellite phone, and that US forces had waited until it was safe to attack him without causing harm to civilians.

Such coups show what 21st century technology can do. But it has been argued that the US is too dependent on gadgetry, at the cost of "human intelligence" - eyes on the ground. Last week's strike in Somalia was based on information from the Ethiopians, who carried out at least two air raids of their own, and the outcome is a matter of bitter dispute. The picture painted at the beginning of the week - of a band of Islamist extremists and terrorists trapped on Somalia's southern border with Kenya, hemmed in by Kenyan forces securing the frontier, US navy vessels offshore and the rapidly advancing Ethiopians and their allies - seemed by the weekend to be fanciful.

The targets of the US air strike were one or more of three top suspects in the bombings of US embassies in Tanzania and Nairobi - Comoros national Fazul Abullah Mohammed, Kenyan Saleh Ali Saleh Nabhan and Abu Talha al-Sudani, from Sudan. It was initially reported that Mohammed, allegedly being shielded, along with the other two, by the Union of Islamic Courts, had been killed. But the claim was later dismissed.

And, as has happened many times with covert US strikes against suspected terrorists, witnesses said dozens of civilians had been killed in the attacks by the US and Ethiopian forces.

Equally routinely, the US denied its strike had killed any civilians. But Moalim Adan Osman, an elder in the village of Dhobley, told Agence France Presse: "We estimated about 100 innocent civilians have been killed. Some are still missing, and I think their bodies are somewhere in the forest." He added: "The airplanes have bombed large areas ? They have bombed the nomads indiscriminately."

US special forces were sent into the far south of Somalia to check whether they had killed their targets - the first time American troops are known to have entered the country since 1993's disastrous Black Hawk Down mission, which saw 18 US army Rangers killed. But it followed two years of covert missions along the SomaliaEthiopia border, carried out with Ethiopian forces. When these failed to locate the suspects they wanted, the Americans turned to new allies inside Somalia - ironically, the same warlords that forced them out more than a decade ago.

US intelligence officials visited Mogadishu several times in 2005 and 2006, handing over suitcases stuffed with $100 bills to chieftains who had formed themselves into an "anti-terror coalition". But the warlords, already unpopular, lost all support when Somalis realised who was funding them. In June, the Islamic Courts, a loose grouping of both moderate and extreme Islamists, drove the US-backed forces out of Mogadishu.

The courts proved popular, delivering a semblance of law and order. But neighbouring Ethiopia was never comfortable with the possibility of a radical Islamist state on its doorstep, and the weak Somali government, based in the small western town of Baidoa, was equally keen to prevent its rivals taking over the whole country. Despite its public opposition, the US fully supported the Ethiopians' Christmas invasion.

What this somewhat chaotic episode shows is that high-tech capability requires high-quality intelligence to be effective. It also requires a more subtle US policy than simply dividing forces in failed states into "good guys" and "bad guys".

Pointing out the pitfalls of relying on regional allies for information, especially when large sums of money are involved, a Somalia expert in Nairobi said: "The Kenyans are quite naive about the situation on the ground in Somalia, and Ethiopia is pursuing its own national interest.

There is heavy emphasis on faulty intelligence.

The US is being milked - that's why there were so many civilian casualties."