The Opposition Liberals have asked federal Auditor General Sheila Fraser to conduct an audit into the government’s cost estimates of $930 million for security measures at the upcoming G8 and G20 summits.

Police officers stand outside the London Stock Exchange in central London's financial district ahead of last year's G20 summit.

In a letter sent to Fraser on Thursday, Liberal MP Mark Holland writes that the projected cost for security is more than the final price tag for security during the Vancouver Olympics, and almost six times the $190 million spent for the two-day G8 summit in Kananaskis, Alta., in 2002.

"While we do not dispute the fact that effective and efficient security is vital when world leaders are involved, we believe this amount to be excessive," Holland wrote.

Federal documents show the cost of hosting the G8 and G20 summits next month in Ontario now stands at $1.1 billion and further outlays are likely.

Security costs at summits G8 summit Japan October 2008: $381 million

G8 summit Gleneagles. Scotland July 2005: $110 million

G20 summit London April 2009: $30 million

G20 summit Pittsburgh, September 2009: $18 million

The price tag includes $160 million for hospitality, infrastructure, food safety and extra staffing. That amount is in addition to the $933-million security bill the Tories revealed earlier this week.

The cost estimates, Holland wrote, are more than 20 times the total reported cost for the G20 summit in Britain in April 2009.

The government insists it has budgeted for the amount. Public Safety Minister Vic Toews defended the spending as as the "most efficient and effective" use of public money for Canada's "unprecedented" hosting of back-to-back international summits amid a medium security threat level.

Toews said the government has followed the advice of security experts and has an obligation to protect visiting dignitaries from around the world.

"The cost is expensive, but the security is worth it," Toews told the House of Commons during Thursday's question period.

Toews also cited the recent firebombing of a Royal Bank branch in Ottawa as a "prime example" of why Canada needs to be "prepared to face thugs and terrorists who threaten our safety."

But Holland blamed the "skyrocketing" cost on "improper planning and foresight" on the part of the Conservative government, which changed the site of next month's G20 meeting from Huntsville, Ont., to Toronto. The G8 summit is being held in central Ontario's Muskoka region.

The Conservatives, he said, should have seen from the start the "challenges" Huntsville presented, and found a more "practical and affordable solution" — other than downtown Toronto.