02/17/2015 09:02 EST | Updated 04/19/2015 05:59 EDT

Iraq mission costs could top $166M for 6 months: budget watchdog

The total cost for Canada's six-month military mission in Iraq could top $166 million, according to a new report from the federal budget watchdog.

That's over $40 million more than the interim estimate released by Defence Minister Jason Kenney on Monday.

A report released by the Parliamentary Budget Office on Tuesday concludes "the estimated incremental cost of Operation IMPACT for six months ranges between a high of $166.40 million and a low of $128.80 million."

Extending the mission for an additional six months could result in a final tab of between $242 million and $351 million.

The report was prepared in response to requests from New Democrat defence critic Jack Harris and his Liberal counterpart, Joyce Murray.

Late Monday, Kenney issued a statement pegging the costs to date at "approximately $122 million," a number he indicated would be included in the next batch of estimates, which are expected to be tabled later this week.

In a written statement, 'Kenney was careful to describe the costs as "incremental," and called it "entirely reasonable," given the importance of the mission.

"Canadian Special Operations and our Royal Canadian Air Force are having a meaningful impact against this genocidal terrorist organization, the so-called ‘Islamic State,'" Kenney added.

"Obviously, if we decide to bring our troops back or extend the mission, there would be additional costs and we would seek further approval from Parliament."

Defence refused to turn over key info: report

Tuesday's report points out that the full costs for the mission in Libya "were almost six times the reported incremental costs."

It also takes the Department of National Defence to task for refusing to turn over information requested by the budget office.

"While DND provided PBO with some information, the majority of PBO’s requests went unfulfilled," the report notes.

"DND made it clear that it took a very narrow view of PBO’s right to access information under the Parliament of Canada Act and would provide information only where it interpreted there to be a clear legal obligation under that act to do so."

As a result, the PBO "had little option, in many circumstances, but to extrapolate from past missions and operations," which "introduces substantial uncertainty into the analysis."

Last November, then Defence Minister Rob Nicholson declined to provide any detail on the cost of the mission.

"[The costs] will be reported, you know, in the normal way," he told MPs on the House defence committee.

"This is a six-month mission, and when the costs are known, we will table them in the usual way."