Canada's associate defense minister on Tuesday said one of the most ardent supporters of the F35 program could back out of a multi-billion purchase of the fighter jets.

"We have not as yet discounted the possibility of backing out of the program," Minister Julian Fantino, responsible for military procurement, was quoted as telling the House of Commons defense committee.

According to Canadian media, he said the government remains committed to buying the jet, but noted that no contract has been signed.

Fantino was not available to confirm the comments, which were widely interpreted as a step back from Ottawa's clarion defense of the costly F35 program.

The Joint Strike Fighter is supposed to form the backbone of the future US air fleet and 11 other allied countries have joined the program.

But defense officials have struggled to keep costs under control, with each plane's price tag doubling in real terms over the past decade.

Ottawa has budgeted Can$8.5 billion to buy 65 F35 fighter jets plus another Can$7.5 billion for lifetime maintenance.

Last month, Prime Minister Stephen Harper said his government would not spend more than this amount for new fighter jets, leaving open the possibility of scaling back the number of jets it buys to stay within budget.