CALGARY — Two U.S. senators are demanding an explanation from U.S. Secretary of State Hillary Clinton, who last week suggested she was “inclined to” approve the controversial Keystone XL crude oil pipeline.

At a speaking engagement in San Francisco last Friday, Clinton was challenged on the State Department’s decision to approve Enbridge Inc.’s (TSX:ENB) Alberta Clipper pipeline, which ships oilsands crude to Wisconsin. Construction wrapped up on Alberta Clipper this spring.

Clinton responded by saying a decision had yet to be made on another pipeline, presumably referring to a US$7-billion extension to rival TransCanada Corp.’s (TSX:TRP) Keystone system, which is currently under review.

“We’ve not yet signed off on it. But we are inclined to do so, and we are for several reasons,” Clinton said last Friday.

She said the United States would either be dependent on “dirty oil” from the oilsands or from the Gulf of Mexico — the site of the worst oil spill in U.S. history — until the country “gets its act together” on renewable energy.

State Department spokesman Mark Toner said Thursday that Clinton’s comments stand.

“We need to, frankly ... find energy sources in other areas as well, be they clean or dirty,” he said.

On Thursday Mike Johanns, a Republican senator from Nebraska, and Jeff Merkley, a Democratic senator from Oregon, said Clinton must clarify what she said during a question-and-answer session at the Commonwealth Club of San Francisco.

Johanns, who had previously expressed concerns over the pipeline’s route, wrote a letter to Clinton in which he called her remarks “premature.”

“While you acknowledged that you haven’t finished all of the analysis and your staff indicated they are still reviewing ’the thousands of comments we have received,’ your comment that the State Department ’is inclined’ to grant approval for the pipeline appears to prejudge the outcome as a foregone conclusion,” Johanns wrote.

“A premature decision of this magnitude is unfortunate, especially in light of the significant concerns I outlined to you in a letter the previous day regarding the proposed pathway of this pipeline,” he said.

Nebraska is one of six U.S. states Keystone XL would traverse on its way to the Texas coast, where numerous refineries are hungry for Canadian heavy crude.

Nebraska Gov. Dave Heineman last week wrote to Clinton, expressing concern that the Ogallala Aquifer — a key water source for the region — could be contaminated if a leak were to occur.

“Maintaining and protecting Nebraska’s water supply is very important to me and the residents of Nebraska,” the Republican governor wrote.

“This resource is the lifeblood of Nebraska’s agriculture industry.”

The fact that Republicans and Democrats alike are concerned shows the issue won’t go away after midterm elections in less than two weeks, said Tony Iallonardo of the National Wildlife Federation.

“Both sides appear to be concerned on the merits of the issue.”

Keystone XL needs the approval of the State Department since the pipeline would cross the Canada-U.S. border.

TransCanada is hoping to get a Presidential Permit giving the project a green light some time early next year, said company spokesman Terry Cunha.

He said TransCanada will go to great lengths to make sure the Ogallala Aquifer is protected.

“We are planning on building the safest pipeline currently in the industry,” said Cunha, noting several pipelines already criss-cross the area.

“We have emergency response plans in place that if something did occur we’d be able to respond immediately. Our system has been designed so if we do detect a drop in flow or pressure on the pipeline, we’re able to shut down and isolate that pipeline within minutes.”

Keystone XL would create 13,000 jobs, bring US$20 billion into the American economy and reduce the country’s reliance on oil from unfriendly countries, Cunha said.

The department extended its review of the pipeline past its mid-September deadline at the insistence of the Environmental Protection Agency and Henry Waxman, a powerful California congressman who has been the most bitter foe of the oilsands on Capitol Hill.

Waxman, chairman of the House of Representatives’ energy and commerce committee, said Clinton’s department was failing to consider the impact that additional oil consumption in the United States would have on climate change.

Safety concerns came to the fore this summer, when two Enbridge crude pipelines in the U.S. Midwest leaked.