OPERATION Flintlock has begun. American special forces have been descending on Burkina Faso, Mali, Mauritania and Senegal in a joint exercise, expected to last another week or so, to combat Islamist terrorism in the region. It is the latest stage of an evolving partnership between America and much of west Africa. Over several years, Americans have been training their counterparts in these countries in everything from marksmanship and parachuting to the more touchy-feely stuff of winning over hearts and minds.

When the Americans first started talking about al-Qaeda's threat in the Sahara, many were sceptical. But a sharp increase in the rate of attacks in the past 18 months by what the jihadists call “al-Qaeda in the Islamic Maghreb”, usually abbreviated to AQIM, have convinced even cynics that a threat of sorts does exist.

When AQIM emerged three years ago out of a ruthless Algerian guerrilla outfit called the Salafist Group for Preaching and Combat, better known by its French abbreviation GSPC, it seemed intent on uniting north African jihadists to wage war on Europe. It has largely failed on that score, having been squeezed by Algeria's security forces, who have broken up many of its cells. Instead, the group is now concentrating on softer targets in a belt of countries farther south.

Armies in the Sahel, that wide stretch of land just south of the Sahara, have increasingly often clashed with Islamist fighters. A handful of Westerners have been killed and a dozen of them who had been kidnapped in the region last year ended up in the hands of AQIM. It is not clear how many of those seizures were carried out by the group's own fighters, thought to number a few hundred, rather than freelancers who passed them on. But ransom payments have certainly swelled AQIM's coffers. Though payments are never officially confirmed, negotiators speak of millions of dollars changing hands to free captives. AQIM is still holding two Spaniards. Only one hostage, from Britain, whose government refuses to pay ransoms to terrorists, has been killed.

Like other rebellious types in the region, such as the Tuaregs of Mali and Niger, AQIM's fighters have long blurred the lines between Islamist militancy and organised crime. Kidnapping is a relatively new business and follows years of smuggling illicit goods across the Sahara to Europe. In recent years Latin American drug gangs have been funnelling a lot of cocaine through west Africa, making the trans-Saharan route far more lucrative. An American-led sting operation in Ghana and the discovery of a burnt-out Boeing aircraft in the desert in Mali have led to claims that AQIM has a big role in the drug trade.

Drug and security specialists say the Islamists are just one of several groups involved. But AQIM is plainly rattling several governments. It plays on local grievances. Its bountiful cash is a lure to young men living in poverty in the desert. The authorities of northern Nigeria are especially worried. The country was the original home of the young man with explosive underpants who tried to blow up an American airliner over Detroit at Christmas.

An additional worry for Western governments is that the AQIM threat may have widened divisions within the region. Algeria is frustrated by the apparent inertia and alleged lack of backbone shown by some of its southern neighbours. Mali, for instance, was accused of feebleness when it freed some Islamists earlier this year in exchange for a French hostage. In the coming weeks the co-operation between American trainers and local security forces will be rigorously tested.