PERSIAN GULF -- Canadian military aircraft are once again over the skies of Syria, helping to identify targets in the fight against the Islamic State of Iraq and the Levant months after the Liberals pulled fighter jets from the mission.

It has been one year since Canadian CF-18 fighter jets flew their last mission over Syria after the Liberals withdrew the planes in favour of a mission to train local forces and help rebuild areas affected by fighting.

While the revamped mission against ISIS includes a mandate to operate over Syria, military officials have been reluctant to confirm whether Canada's surveillance and refuelling planes are operating over the country.

Two Canadian surveillance planes have flown hundreds of sorties to identify potential targets for coalition airstrikes, the majority of which have been in Iraq.

On Sunday, a senior Canadian commander revealed that the aircraft have also quietly flown dozens of times over Syria in recent months.

"We have done work in Syria," Brig.-Gen. Shane Brennan, commander of Canada's Joint Task Force-Iraq, told reporters during a media tour of the mission, though he added: "There's lots of work to do in Iraq. We are looking at all of the areas."

Brennan spoke at an airfield, the location of which the military didn't want revealed for security reasons, where reporters were given an exclusive tour of one the surveillance planes.

The CP140 Aurora was originally designed during the Cold War to detect Soviet submarines, but has since been upgraded to provide enhanced photos and other imagery of ground targets as well.

Canadian military intelligence officers at the base carefully review the images for targets, as well as schools, hospitals, mosques and other structures considered too sensitive to hit. When officers identify a target, they pass the information to coalition forces for additional verification before a strike mission is assigned.

The flights over Syria have also included a different Canadian plane that has been refuelling coalition aircraft directly responsible for bombing ISIL forces and other targets.

The increased Canadian military activity over Syria, which Brennan described as between 20 and 30 missions in the past few months, is one indication that the war against ISIS is shifting into a new phase.

As Brennan heaped praise on the work of Canadian and Iraqi troops, Iraqi forces were launching their long-awaited assault on western Mosul.

The battle, which comes about a month after Iraqi forces declared the eastern part of the city free of ISIS, has been billed as a defining moment in eventually freeing Iraq from the extremist group's grip.

While the fight for the city's western half is expected to be much harder than what came before, Brennan was adamant that victory was a certainty.

"There is a battle that is ongoing and will be won," Brennan said. "It's an inevitable event."

Less certain is what role Canadian troops will play when the current mandate, which also includes a military hospital, special forces troops and a helicopter detachment in northern Iraq, expires in March.

More than 800 service members are currently deployed in half-a-dozen locations across the Persian Gulf region after the Liberal government revamped Canada's contribution to the American-led war against ISIS last year.

Military commanders are drawing up options based on a number of factors, including the expectation that ISIS will become a traditional insurgency in Iraq, which would require more police and counter-terrorism forces.

Canadian Brig.-Gen. David Anderson, who is leading an international team of military advisers in Iraq's defence ministry, said his group recently submitted a two-year plan focused on exactly that.

There are also concerns that the group will try to spread outside Iraq and Syria, which is why Canada is helping to strengthen border security in Jordan and Lebanon.

The military will present three options for the government to choose from in the coming weeks in deciding the future of the mission.

Yet one big wild card is what direction the U.S. military will go after President Donald Trump blasted the slow progress of the fight against ISIS and ordered a 30-day review to consider new options.

U.S. Defence Secretary James Mattis is expected to visit Iraq in the next week or so before presenting his recommendations later this month.

Exactly what Mattis will recommend, both in Iraq and Syria, is wide open for speculation.

Brennan said the results could have a big impact on what Canada decides to do given the need to ensure a unified and co-ordinated international effort in the fight against ISIS.

"It does depend what happens," Brennan said. "We are waiting as well. I think the question is: What else needs to be done, or could be done?"