The U.S. State Department has rejected TransCanada's request to put the review of the proposed Keystone XL pipeline on hold.
Spokesman John Kirby said the department wrote to TransCanada on Wednesday and "communicated our decision to continue our review."
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Mark Cooper, a spokesman for TransCanada, said that the company respects the State Department's decision.
The State Department has jurisdiction over the pipeline because it crosses a U.S. border. The proposed pipeline would carry crude oil from Alberta to the U.S. Gulf Coast.
Democratic presidential hopeful Bernie Sanders, who is challenging Hillary Clinton for the presidential nomination, has urged President Barack Obama to reject the long-delayed pipeline before heading to Paris next month to finalize a global climate agreement.
The company sent a letter to Secretary of State John Kerry on Monday, saying it believes there is precedent for making the request to pause the review.
TransCanada's letter had asked the U.S. government to delay its decision on a border-crossing permit, until after the resolution of a dispute in Nebraska over the route which could take another nine months to a year.
Most analysts believed the request was an attempt to forestall a veto of Keystone by Obama, who will be looking to build his environmental credentials ahead of the Paris climate summit.
Cooper said TransCanada's efforts will "continue to demonstrate that Keystone XL is in the national interest of the United States — just as five reports and 17,000 pages of State Department review have demonstrated over the past seven-plus years."
"We will continue to focus on building a pipeline that will put 2,200 Canadian construction workers and 9,000 in the United States to work, not to mention tens of thousands more on the full value chain that the State Department itself identified in its review," Cooper said.