Former U.S. Secretary of State Hillary Clinton said Ottawa's offer to co-operate with the United States on reducing oil and gas-related carbon emissions is a welcome development, though she steered clear of predicting how the contentious Keystone XL pipeline might fit into that pledge.

Ms. Clinton told a Calgary business audience anxious for hints on the fate of the pipeline that Canada and the U.S. should work together on an energy and climate pact that could serve as a starting point for one that encompasses the entire Western Hemisphere.

In a letter to current Secretary of State John Kerry late last month, Gary Doer, Canada's ambassador to the U.S., said the Harper government wants to work with Washington on curbing energy-related pollution. The letter also urged approval of TransCanada Corp.'s Keystone XL oil pipeline to the southern U.S. from Alberta, now in its sixth year of regulatory review.

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"I think that was a very welcome offer by Prime Minister Harper, by your ambassador, to begin such a discussion," said Ms. Clinton, seen as a front-runner for Democratic presidential nominee in 2016, but as-yet undeclared.

"I think the opportunity for the United States and Canada to co-operate on both energy and the environment – and it has to be together, not one or the other – is unprecedented and would give both of our countries an opportunity to really take the lead globally in producing energy in sustainable, safe ways that do not harm the environment, and also taking steps to try to prevent and mitigate the effects of climate change," she said.

In January, a State Department environmental assessment concluded that the pipeline, aimed at feeding refineries on the U.S. Gulf Coast with Canadian crude, would not significantly increase greenhouse gas emissions. Mr. Kerry's department is weighing an approval decision, as it did when Ms. Clinton was secretary. President Barack Obama has final word, though he has no firm deadline.

She declined to answer a question from a former Canadian ambassador to Washington, Frank McKenna, on whether the lengthy delay is being driven by U.S. politics, and if Canada could expect an answer soon.

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Prime Minister Stephen Harper has described a U.S. approval as a "no-brainer" given the project's promise of jobs and energy security on both sides of the border. More recently, Foreign Affairs Minister John Baird showed the government's frustration with the plodding process, saying, "The time for a decision on Keystone is now, even if it's not the right one. We can't continue in this state of limbo."

Ms. Clinton described the U.S. review as "very comprehensive," taking into account concerns of various states as well as prospects for jobs, impact on climate and other aspects.

"Ultimately, Sec. Kerry will have to make that decision. And I think it's important not to let whatever that decision is on one pipeline colour the potential for co-operation across the board between the United States and Canada on energy production and climate change," Ms. Clinton said.

The speech to 2,500 people on Thursday morning followed an evening talk in Vancouver. In both cities, she criticized Russia's incursion into Ukraine and the tactics of Russian President Vladimir Putin.