Americans are being misled with an "overstimulated environmental argument" on the Keystone XL pipeline, according to a former Liberal prime minister who plans to visit Washington to lend his voice to ongoing Canadian lobby efforts in support of the controversial proposal.

John Turner, 83, who served briefly as prime minister in 1984, said Monday he will soon be joining Gary Doer, Canada's ambassador to the United States, to speak with members of Congress, other government leaders, and ideally – though he admits it's unlikely – President Barack Obama.

"I believe in Keystone," Mr. Turner told a business audience in Calgary, Canada's energy capital. "I'll be going down to Washington to talk about that. We've got to get the Americans to understand that they've got a friendly neighbour up here."

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The proposed Keystone XL pipeline, with an estimated price tag of at least $5.3-billion, by Canadian company TransCanada Corp., would bring crude from the oil sands in northern Alberta to the U.S. Gulf Coast. But the concept has been met with opposition, largely from environmental groups.

Mr. Turner, who is planning his visit as a "private citizen," said he hopes to set straight some misinformation and explain that Canada offers a long-term supply of reliable crude that can be produced in an environmentally responsible manner. "They're hearing an overstimulated environmental argument," he said of the U.S. naysayers.

Although using a walker to help get around, Mr. Turner remains feisty in his political views, and his frustration with U.S. delays is clear.

"When they look at the Canadians, compared to the other sources of those resources – the Middle East, for God's sake. Turmoil. Unending. No possibility of a resolution. Venezuela. Always in a shambles. Good God. What are you Americans talking about? … Let's get with it, guys. That'll be my message in Washington."

Mr. Turner was a senior cabinet minister under former prime minister Pierre Trudeau. He left politics, but returned to win the leadership in 1984 and served for nearly three months as prime minister, before losing decisively to Brian Mulroney's Progressive Conservatives. He retired from politics for good in 1990.

There have been no signs of other former prime ministers, including Mr. Mulroney, Jean Chrétien, Paul Martin, Kim Campbell or Joe Clark, publicly weighing in on Keystone.

Current provincial and federal leaders have made multiple trips to the U.S. to speak up for the project. Mr. Turner singled out Alberta Premier Alison Redford for making four trips to Washington, but said more could be done.

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Joe Oliver, the federal Conservative natural resources minister, praised Mr. Turner for keeping a hand in current events. "We are encouraged that prominent Canadians, including former Prime Minister John Turner, are supporting our government's position that Keystone XL should be approved on its merits," he said in a statement from Israel, where he is travelling.