More than half the U.S. Senate on Wednesday urged quick approval of the Keystone XL oil pipeline, ramping up pressure on President Barack Obama to move ahead with the project just days after he promised in his inaugural address to respond vigorously to the threat of climate change.

A letter signed by 53 senators said Nebraska Governor Dave Heineman's approval of a revised route for the pipeline puts the long-delayed project squarely in the president's hands.

"We urge you to choose jobs, economic development and American energy security," the letter said, adding that the pipeline "has gone through the most exhaustive environmental scrutiny of any pipeline" in U.S. history.

The $7 billion project would carry oil from Canada to refineries along the Texas Gulf Coast.

"There is no reason to deny or further delay this long-studied project," said the letter, which was initiated by Senators John Hoeven, a Republican, and Max Baucus, a Democrat, and signed by 44 Republicans and nine Democrats.

Another Democrat, Jon Tester of Montana, supports the pipeline but did not sign the letter.

At a news conference Wednesday, senators said the pipeline should be a key part of Obama's "all of the above" energy policy, in which he has expressed support for a range of energy sources from oil and natural gas to wind, solar and coal.

Approval blocked twice

The Obama administration has twice thwarted the 2,700-km. pipeline, which Calgary-based TransCanada first proposed in late 2008.

The State Department delayed the project in late 2011 after environmental groups and others raised concerns about a proposed route through environmentally sensitive land in Nebraska.

Under pressure from congressional Republicans to make a decision on the pipeline, Obama blocked it in January 2012, saying his concerns about the Nebraska route had not been resolved.

TransCanada submitted a new application last spring.

The State Department said Tuesday it does not expect to complete a review of the project before the end of March.

The State Department has jurisdiction over the pipeline because it crosses a U.S. border.

The renewed focus on the pipeline comes as Obama pledged during his inaugural address to respond to the threat of global warming. Environmental groups and some Democratic lawmakers argue that approving the pipeline would directly contradict that promise.

House Speaker John Boehner says all six states along the route now support the project. (Yuri Gripas/Reuters)

"If we are going to get serious about climate change, opening the spigot to a pipeline that will export up to 830,000 barrels of the dirtiest oil on the planet to foreign markets stands as a bad idea," said Anthony Swift of the Natural Resources Defense Council.

The pipeline would carry heavy oil derived from the oilsands of Alberta. The heat-intensive process uses more energy than traditional oil, producing more heat-trapping gases that contribute to global warming.

Environmental groups have been pressuring Obama to reject the pipeline, citing the oil's high "carbon footprint." They also worry about a possible spill.

At a news conference Wednesday, senators from both parties said the Nebraska decision leaves Obama with no other choice but to approve the pipeline, which would carry up to 800,000 barrels of oil a day from tar sands in western Canada to refineries in Houston and other Texas ports.

The pipeline also would travel though Montana, South Dakota, Nebraska, Kansas and Oklahoma.

"No more excuses. It's time to put people to work," Baucus said.

"Back home, we call this a no-brainer," added Democratic Senator Joe Manchin.

Hoeven, of North Dakota, said the oilsands oil will be produced whether or not the U.S. approves the project.

Polls suggest majority support

"Our choice is, the oil comes to us or it's going to China," he said.

Nebraska's approval of the pipeline means all six states along the proposed route now support the project, said Republican House Speaker John Boehner. Majorities in the House and Senate also have endorsed the pipeline.

National polls repeatedly show a majority of Americans back the pipeline.

Boehner said he recognizes the political pressure Obama faces from environmental groups and other opponents, but said "with our energy security at stake and many jobs in limbo, he should find a way to say yes."

White House spokesman Jay Carney said Tuesday that the State Department was reviewing the project and he did not want to "get ahead of that process."

Once that review is completed, "we'll obviously address that issue," Carney said.

Meanwhile, Secretary of State nominee John Kerry said he plans to divest holdings in dozens of companies in his family's vast financial portfolio to avoid conflicts of interest if he is confirmed by the Senate.

Kerry, a Massachusetts Democrat, said he would not take part in any decisions that could affect the companies he has holdings in until those investments are sold off.

Among the investments are holdings in two Canadian companies, Suncor and Cenovus Energy Inc., both of which have publicly supported the Keystone XL pipeline. Kerry's investments are in family trusts.