OTTAWA - Canadian warplanes escorted an Australian transport on a humanitarian airdrop mission over a besieged portion of northern Iraq, the military revealed Thursday.

The C-130J transport delivered 32 tonnes of relief supplies in four drops to beleaguered civilians on Mount Sinjar, where minority Yazidis remain stranded months after being driven from their homes by Islamic State fighters.

The flights, which took place between Nov. 20-23, delivered water, tents and blankets to the civilians, who must now confront the onset of winter in the rugged, 65-kilometre long mountain strip.

The relief comes as Kurdish peshmerga fighters prepare for a large-scale offensive to relieve the siege, which began in August, capturing the attention of western media and helping to spur the initial U.S. intervention.

The Canadian military was at first reluctant to say much about the operation despite the fact that the Australian defence department and media outlets had already reported in detail on Wednesday about the mercy flights.

Col. Dan Constable, the officer in charge of Canada's task force in Iraq, cited operational security Thursday as he refused to tell a teleconference where the mission took place, when it happened or at whom it was aimed.

"The presence of our CF-18s to provide top cover for the transport aircraft allowed it to deliver its aid cargo at a lower altitude, knowing that our fighter aircraft could detect and target any air or ground threats," Constable said from an undisclosed base in Kuwait, where Canada's contingent has been operating.

"The mission was highly effective, and appreciated by our coalition partner."

He said since another country was involved and there was the possibility the planes might return to the area, details are considered a matter of operational security.

But late Thursday, a spokeswoman for the military's operational command confirmed in an email that the airdrops were in support of the Australians.

It's not the first time the Canadian military has been slow in providing sanitized operational details. The U.S. command overseeing the coalition mission trumped the government by 24 hours in announcing details of the first bombing mission involving CF-18s three weeks ago.

That disclosure hesitancy comes at a time when opposition parties are still smarting from the Harper government's refusal to release even a preliminary cost estimate for the campaign.

The cost "will be reported in the normal way; usually within 90 says of the completion of a mission the costs are tabled," Nicholson told the Commons defence committee on Tuesday.

Liberal defence critic Joyce Murray said the inability or the unwillingness of the government to account for even the most basic details of the combat mission is becoming a major concern.

"It's not acceptable and there's no reason to hide from Canadians," Murray said. "Our allies in Australia and the UK are providing timely briefings about their missions as well as cost estimates."

Releasing little or no information is a political tactic designed to frustrate those who are questioning the effectiveness of Canada's campaign against the Islamic State of Iraq and the Levant, said NDP defence critic Jack Harris.

"It's obvious these guys have been told to zipper up," said Harris.

The CF-18s have flown a total of 72 combat missions since the beginning of the campaign, four of which have resulted in bombing runs.

The Canadian contingent gets its strike orders and missions from the U.S. coalition command, headquartered in Qatar, Constable repeated during Thursday's call.

The dearth of targets is partly due to Islamic State fighters concealing their movements — a challenge that could get more difficult as the U.S. moves more aircraft into the region, as planned.

The New York Times reported Wednesday that low-flying A-10 attack jets and surveillance aircraft are being moved from Afghanistan to bases in Kuwait to join the air war in direct support of Iraqi forces.

News from © The Canadian Press, 2014