Bloc Québécois Leader Gilles Duceppe vowed Thursday — in the wake of the deaths of three Quebec-based soldiers this week — to bring down the Conservative government if it does not commit to a full troop withdrawal from Afghanistan in 2009.

He said if Prime Minister Stephen Harper does not soon notify NATO and participating countries of Canada's withdrawal plans, the Bloc will vote against the expected autumn throne speech with the hopes of bringing the government down.

Duceppe would need the Liberals to vote with his party in order to succeed.

During a Thursday press conference on climate change, Liberal Leader Stéphane Dion would not comment about banding with the Bloc.

"I am not here to make threats about that," he said. "I don't want to play politics on the back of the victims."

Duceppe called for an emergency debate on the Afghan mission when Parliament reconvenes on Sept. 17.

Duceppe said, in a French statement, that he shared in the sadness of the families, friends and colleagues of the soldiers and offered his sincere condolences.

"All families who have a brother, a wife, a father in Kandahar must be feeling this sadness," he said. "These latest victims in the Afghan conflict remind us of the dangers and the difficult conditions under which soldiers working in the theatre of combat are exposed."

On Wednesday, Master Warrant Officer Mario Mercier and Master Cpl. Christian Duchesne, both based out of Valcartier, were killed in a blast about 50 kilometres west of Kandahar following a fierce battle with insurgents.

An Afghan interpreter was also killed in the blast, while Radio-Canada cameraman Charles Dubois suffered a serious leg injury and reporter Patrice Roy was treated for shock.

News about the most recent deaths broke as the body of 23-year-old Pte. Simon Longtin arrived in Canada. Longtin died Sunday after his light-armoured vehicle was hit by a roadside bomb.

In light of the most recent deaths, which brought the Canadian death toll in the Afghanistan mission to 69, Duceppe said the government must commit to a full troop withdrawal in February 2009.

Dion repeated his position that Harper should immediately notify NATO that Canada will withdraw its troops.

"Why does Mr. Duceppe want to wait until October? I'm asking the prime minister to notify NATO, the government of Afghanistan that the combat mission in Afghanistan will end in February 2009," Dion said. "Let's do it today. Why wait until October?"

He said it was important to notify NATO now to give its partners time to replace the Canadian contingent.

Charest makes call for support of troops

Quebec Premier Jean Charest, meanwhile, called on Quebecers to support their troops in Afghanistan in the wake of the recent deaths.

"It's one thing to have a view about war, about engaging," Charest said Thursday from a conference in Kuujjuaq in northern Quebec. "But once the Parliament of Canada decides that we're going in ... we have to support the soldiers that fulfill that mission in our name, who risk their lives."

Charest said the deaths were a tragedy for both the families and for the country.

"We're very saddened by the lost of the soldiers, and yesterday's event also reminded us that journalists also risk their lives in covering these events," he said. "We hope that Mr. Roy and his cameraman will be safe and will be OK."

Harper released a statement calling Wednesday "a very sad day" and extending his sympathy to the families.

"We are all proud of these exceptional Canadians and grateful for their sacrifices," he said. "These soldiers gave their life helping to bring stability and security to Afghanistan. We will always remember them."