OTTAWA -- The massive Canadian C-17 transport plane that's currently ferrying French war supplies to Mali has been seconded from regular duty in Canada and elsewhere for the next three months.

The decision by air force planners offers further evidence the Conservative government is poised to extend its commitment to what observers say could be a prolonged battle against Islamic extremists who've dug themselves into the northern half of the former African colony.

The transport, which is attached to 429 Squadron out of CFB Trenton, has been flying vehicles and equipment between France and the Malian capital of Bamako in a deployment Prime Minister Stephen Harper said would only last a week.

Defence sources say the overseas command running the operation has not been notified of an extension; a spokesman for Defence Minister Peter MacKay says the government's commitment has not changed.

That commitment is set to expire Thursday, but Harper is expected to announce an extension any day now.

Setting aside the single C-17 Globemaster III for three months does not automatically mean a government extension would last that long, but it gives both the air force and the Conservatives flexibility to deal with an evolving crisis.

What remains unclear is whether the Conservatives are prepared to offer other assistance in the form smaller transport aircraft, such as the newly purchased C-130J Hercules.

The mission could evolve into helping move African troops from neighbouring countries into Mali, defence sources suggest. Late last year, the UN approved a 3,300-member intervention force to be drawn from nations in the region.

French Foreign Minister Laurent Fabius has said Canada had offered to keep flying the C-17 in support of the military operation, which began Thursday with the arrival of French troops. Fabius made the comments on the weekend after French President Francois Hollande appealed to Harper for additional help.

French forces have reported some success in turning back the advance of al-Qaida in the Islamic Maghreb (AQIM), an offshoot of Osama bin Laden's al-Qaida which took over the northern portion of Mali last March.

Not only has it imposed its strict version of Islam in the vast desert territory, which is about the size of France, the group has also established training camps and weapons stockpiles in towns and at former government bases.

Intelligence reports coming out the region indicate that AQIM rebels have begun digging trench lines around communities and fortifying outposts in what could be a sign they intend to stand their ground against the French, similar to the way the Taliban did against Canadian soldiers in Afghanistan in 2006.

Former Canadian diplomat Robert Fowler said no one should be surprised by such reports, which suggest efforts to dislodge the militants could be long, difficult and demanding of much more firepower than African nations can muster.

"They're tough guys, as the French have found out over the past 10 days," said Fowler, who was held hostage by al-Qaida in north Africa in 2009. "They're extremely focused, tenacious enemies."

It is very clear "a whole bunch of other countries, friends of Africa and friends of the French are going to have to respond," Fowler said.