Islamist militants have mounted a hit-and-run attack against French forces occupying the former jihadist bastion of Gao in what's probably the opening salvo of a long insurgency against North African regimes.

A 4,000-troop French ground force, backed by airstrikes, may have driven back Islamists, who last month thrust out of northern Mali in a push toward Mali's capital Bamako, but they haven't crushed them.

The Islamists, who by several accounts suffered only light casualties since the French began their intervention Jan. 11, have simply melted away in the face of superior firepower and dispersed in the region's deserts and mountains.

The surprise attack by around 10 Islamists in Gao Sunday triggered battles across the city held by French troops and elements of Mali's weak and fragmented army.

Details of the surprise raid remain unclear, but with the French, backed by around 1,000 Chadian troops, spread out so thinly after their month-old offensive, their rear areas were said to be open to attack by fast-moving raiders.

The Gao attackers were reportedly from the radical Movement for Oneness and Jihad in West Africa, or MUJAO, an offshoot of the al-Qaida in the Islamic Maghreb, the region's main jihadist group.

The rugged Adrar des Ifoghas mountains of northern Mali have become the new battleground in the spreading war on terrorism.

These days they're known as Africa's Tora Bora, after the Afghan mountains where Osama bin Laden holed up as he was being driven out of Afghanistan by the invading Americans in December 2001. Obama evaded the U.S. troops and slipped into Pakistan.

A long and bruising insurgency, led by veterans of Algeria's ferocious civil war against Islamists throughout the 1990s, isn't what French President Francois Hollande had in mind when he intervened in Mali, a former French colony.

But as Colin Powell warned U.S. President George W. Bush as he was about to charge headlong into Iraq in March 2003: "If you break it, you own it."

The fighting in Mali, widely seen as a consequence of the 2011 civil war in Libya that toppled Moammar Gadhafi, has raised fears the oil and gas industry, the region's economic mainstay, may be a major target.

But there are other potential long-term threats across Sahel, the semi-arid belt that runs across Africa from the Atlantic to the Red Sea.

French intervention could presage greater foreign involvement which few in the region desire, particularly Algeria.

The fear is that foreign military operations will only drive Muslims into the arms of al-Qaida.

The French advance northward was clearly less a military rout of the Islamists than an orderly strategic withdrawal by them into inhospitable terrain that's ideal for a sustained insurgency, financed by the profits from AQIM's traditional Sahel smuggling operations.

The Islamists have quickly resorted to using roadside bombs, no doubt the work of seasoned foreign veterans who fought in Iraq, Somalia and Yemen.

On Feb. 8, MUJAO carried out a suicide bombing against a Malian army checkpoint near Gao, a former Islamist bastion. The motorcycle-riding bomber killed only himself but the operation, the first suicide attack of the conflict, signaled more to come.

There's growing evidence that retreating Islamists are migrating across a vast region of the Sahara to shelter in the region's dysfunctional states, such as Libya, Mauritania and even Sudan.

There's little these states, poorly funded with unreliable militaries, can do to stop them but this could lead to greater Western intervention.

The French say they plan to start withdrawing from Mali in March. But politically Hollande cannot be seen to cut and run, leaving a smoldering powder keg behind him.

"France will stay as long as necessary," he said Feb. 2 during a visit to Mali, "but its purpose is not to stay."

However, no doubt with the U.S. quagmires in Iraq and Afghanistan in mind, Western leaders say the Sahel conflict has only just started.

British Prime Minister David Cameron says it could last for "decades."

But, as British commentator Philip Stephens observed: "What concerns me is the absence of anything resembling a strategy.

"Intervention is the easy bit. I have yet to hear anyone offer a serious answer to the 'What then?' question."