OTTAWA -- Defence Minister Jason Kenney is now saying the estimated cost of extending Canada's combat mission in Iraq and Syria will be $406 million, and he's instructed his department to include the figures in federal budget reports.

The federal Treasury Board's plans and priorities report for the coming fiscal year, released Tuesday, shows the price tags for overseas operations in both the Middle East and eastern Europe are classified.

Both opposition parties say hiding the figures is unacceptable.

Kenney, however, claims to have already released the numbers, but says the information wasn't available when the budget forecasts were signed off at the beginning of March.

Dave Perry of the Canadian Defence and Foreign Affairs Institute says it's the first -- and only -- time in nearly 20 years that a cost estimate for an international operation was withheld because it was deemed classified.

The budget estimates also show the age of austerity is here to stay at National Defence with baseline budget spending to expected to drop over the long term.