Liberal Leader Michael Ignatieff says he will no longer support Stephen Harper's minority government.

In a speech Tuesday to the Liberal caucus, Ignatieff said Harper's time as prime minister, "is over."

"I cannot support this government any further," Ignatieff said to cheers and wild applause, following a meeting with his Liberal caucus, which is on retreat in Sudbury, Ont.

"We will hold Stephen Harper to account and we will oppose his government in Parliament."

Sources have told CTV News that the Liberals will put forward a non-confidence motion to force an election this fall -- although they need the support of the NDP and the Bloc Quebecois for that to happen.

Speaking in Calgary, Harper said Canadians selected their government when they went to the polls less than a year ago and aren't keen for yet another election.

"I haven't met a single Canadian who is saying they want to see an election right now. I just don't find that," Harper said.

"I think Canadians have been pretty clear. They want Parliament to focus on the economy."

NDP MP Thomas Mulcair agreed with the prime minister, saying "we'd better have a bloody good reason for forcing a fourth general election in five years.

"So if Mr. Harper goes about being provocative as he has been in the past, going after key things that Canadians hold dearly like women's rights and the environment, then we'll throw him out of office because he'll have provoked it," Mulcair said.

"If, on the other hand, Stephen Harper comes into Parliament with a willingness to work in the public interest, then we're going to take it on a case-by-case basis."

Mulcair's cautious words stood in stark contrast to Ignatieff's fiery, campaign-style speech, during which he attacked Harper's record on the economy and other issues.

"Mr. Harper, you have failed all four tests," Ignatieff said. "You've failed to protect the most vulnerable. You've failed to create jobs. You've failed to defend our health care. You've failed to produce a plan to restore our public finances."

Ignatieff said his party "can do better" at managing the economic crisis, protecting Canadians abroad and making the country competitive.

"Stephen Harper doesn't get it," Ignatieff said. "He doesn't get that Canada's in a race -- that we've got to position our country to compete in the 21st century. We've got to make Canada a world leader again -- and we've got to do it now."

Possible September showdown

CTV's Graham Richardson said the Liberals could move to topple the government by putting forward a non-confidence motion on a previously agreed upon opposition day at the end of September.

However, a vote on the ways and means portion of the budget is scheduled for one of the first days after Parliament resumes on Sept. 14, Richardson said, which means the opposition could bring down the government at that time.

"We're talking about timing, and when in fact it's going to happen this fall as opposed to if it's going to happen this fall," Richardson told CTV News Channel.

When Parliament went on summer break, the break down of seats was:

  • 143 for the Conservatives
  • 77 for the Liberals
  • 36 for the New Democrats
  • 48 for the Bloc Quebecois

On Tuesday afternoon, Transport Minister John Baird dismissed questions about working with the NDP, saying that the opposition party hasn't shown "any desire or willingness to work with the government" in the past.

"I think it is most regrettable that we're seeing this kind of political bravado from Michael Ignatieff and the Liberals," Baird said.

Earlier Tuesday, Liberal finance critic John McCallum said that his party isn't satisfied with the Conservative government's management of the economic crisis, saying the Tories were too slow at getting fiscal stimulus money out the door this summer.

"Well I certainly think a strong case can be made for a change in government on grounds of economic mismanagement because yesterday's growth numbers showed that, far from leading the G7 out of recession, Canada was dead last in its economic performance in the second quarter," McCallum told Smith.

'Political brinkmanship'

According to pollster Nick Nanos, Ignatieff and Harper are locked in a game of "political brinkmanship."

Though the leaders have faced-off on political issues before, Nanos said it will be difficult for Ignatieff to stand down this time for fear of appearing weak in the eyes of voters.

Nanos added that the Tories hammered Stephane Dion, Ignatieff's predecessor, with similar accusations during last year's election.

"I don't think (Ignatieff) can turn back, because if he does, the comparisons with Stephane Dion will pop up -- they already have -- in a New York minute," he said.

Still, Nanos said the outcome of a potential campaign will depend on how the parties pick their battles.

"Any kind of election about the economy will naturally favour the Conservatives, because that's part of their core brand strength," Nanos told CTV News Channel Tuesday evening.

He added that the Liberals will benefit from issues like healthcare and national unity, the former which appears to be a growing issue with Canadians once again.

With files from The Canadian Press