WASHINGTON: The United States has chosen to play a cautious supporting role to France's military action against Islamist fighters in Mali, after Washington's own attempt to build up the African nation's army backfired badly.

While the Pentagon promised transport planes, refueling tanker aircraft and spy planes to back up France's intervention in Mali, officials made clear President Barack Obama was deeply reluctant to plunge America into a fresh war against insurgents.

"I think the United States was very cautious not to get involved in another complex operation, which is sold as easier than it actually is," Stephanie Pezard, a scholar at the RAND corporation, told AFP.

"It didn't want to be bogged down on another front that's maybe not of the highest strategic interest either," she added.

But the French military action also raised questions about a much-touted US policy that hopes to counter terror groups in Africa and elsewhere by bolstering foreign armies with advice from elite American special forces.

The US administration had pinned its hopes on shaping a new generation of Malian officers, but some of the units ended up defecting to join insurgent fighters, with weapons and hardware falling into the hands of militants.

And in March last year, an officer who had attended several training courses with the US military, Captain Amadou Sanago, led a coup against the Malian government, prompting Washington to suspend its security assistance.

The outcome was an embarrassment for Washington, which had held up Mali as an promising model for counter-terrorism efforts in the region.

"I was sorely disappointed that a military with whom we had a training relationship participated in the military overthrow of an elected government. I mean, there is no way to characterize that other than wholly unacceptable," General Carter Ham, head of US Africa Command, said last month at Brown University.

After its disastrous experience with the Malian army, the Americans came away chastened and reluctant to back a major military intervention, particularly after more than a decade of mixed results in wars in Afghanistan and Iraq, experts and former officials said.

"The US, having been involved in training the Malian army for a while, knows their capabilities, knows how much work there is left to do," said Pezard.

Some inside the administration have been sympathetic to French calls for direct action, including the US Special Operations Command, which has favored targeting senior figures in the militant groups that have seized control in northern Mali, Al-Qaeda in the Islamic Maghreb (AQIP) and Ansar Dine, The New York Times reported Monday.

But other current and former officials worry that military action will only deliver a temporary respite without political and diplomatic steps to break the link between AQIP and local groups, restore democratic rule and defuse decades-long grievances among the Tuareg community in the north.

In the meantime, US political leaders preoccupied with a mushrooming budget deficit and there is little appetite for an open-ended operation.

"I'm afraid if we go down this road, it's a slippery slope, where we make some serious mistakes that could cost us in the long run," said Rudolph Atallah, a former Africa counter-terrorism adviser at the Pentagon.

"The big question is who is going to fund this long term presence on the ground?" said Atallah, now a senior fellow at the Atlantic Council think tank.

The Obama administration's stance has been similar to its role in the NATO air war against Libya's regime, allowing its French allies to take the lead, though in that case US warplanes took part in bombing runs.

US officials have worried that any outside intervention could inflame Mali and turn it into a recruiting ground for foreign extremists.

But Washington's view of AQIP as a lesser, regional menace has shifted, after the group got hold of weapons in Libya and forged an alliance with the Islamist group Ansar al-Din.

"AQIM has acquired weapons from Libyan caches that probably make it the best armed Al-Qaeda franchise in the world today," according to former CIA officer Bruce Riedel, a fellow at the Brookings Institution.

It was the group's dramatic gains on the battlefield in Mali that raised alarms in recent weeks, experts said, making the US government more open to the French decision to attack the Islamists directly.

The United States had a "cautious" stance, "but that was back in December before the Islamists started advancing south," said Pezard.

"So this has changed lots of things and that may have changed the thinking on the US side as well."