MONTREAL - Bloc Quebecois Leader Gilles Duceppe called Prime Minister Stephen Harper a "liar" Saturday morning during his first speech of the election campaign.

Duceppe said Harper's warning that a coalition of the three opposition parties would be negative for the country runs counter to the prime minister's actions a few years prior.

Duceppe brandished a letter he signed along with Harper and NDP Leader Jack Layton on Sept. 9, 2004, which was destined for then-governor general Andrienne Clarkson.

The letter asks Clarkson to consider all the options at her disposal should Paul Martin's Liberal government lose the confidence of Parliament and fall.

Those options included a coalition government with Harper as prime minister.

"When he tells us that whoever doesn't win the election cannot become prime minister, he wrote the opposite (in the letter)," said Duceppe.

"Exactly the opposite. He lied this morning."

The letter doesn't explicitly mention the possibility of a coalition, but according to Duceppe, he and Harper discussed that option during a meeting.

Duceppe didn't rule out the possibility of the Bloc taking part in a future coalition government.

"I will look at what the situation is after the election," he said.

Harper visited Gov. Gen. David Johnston Saturday morning and asked him to dissolve Parliament. The election is scheduled for May 2.

Harper immediately went into attack mode after leaving Johnston's residence at Rideau Hall. His target: a coalition government comprised of the Liberals, the New Democrats and the Bloc.

"Imagine a coalition of arch-centralists and Quebec sovereigntists trying to work together," he said. "The only thing they'll be able to agree on is to spend more money and to raise taxes to pay for it. It's a risk our country can't take."

Liberal Leader Michael Ignatieff denied his party would join a coalition government.

"We will not form a coalition with the other federalist parties, especially not with the Bloc Quebecois," he said, adding he "categorically" rejects any association with separatists.