A letter signed by 53 U.S. senators has called for action from President Obama in relation to the Keystone XL oil pipeline, urging him to give the project the green light, it has emerged.

Following the long-awaited approval of the Keystone XL oil pipeline by Nebraska Governor Dave Heineman, the go-ahead of the project is back in the hands of the federal government. The letter, signed by 44 Republicans and nine Democrats, stated that the pipeline has already been given extensive environmental scrutiny, more comprehensive than any other pipeline examination in U.S. history. The senators called for President Obama to "choose jobs, economic development and American energy security."

The project, estimated to cost around $7 billion and deemed to be of major strategic importance, would carry oil from the oilsands of Alberta, Canada to refineries situated at the Texas Gulf Coast. The group of senators, spearheaded by Senators John Hoeven, R-N.D., and Max Baucus, D-Mont., claimed that the pipeline construction can no longer be delayed. Speaking at a news conference on January 23, the senators said that the pipeline should be a top priority in the president's energy policy. President Obama has already backed the use of a number of energy sources, ranging from natural gas and oil to wind and solar energy.

However, the Obama administration has already blocked the Keystone XL project twice after it was first proposed in 2008. The initial plans were presented by TransCanada, which claimed that the construction of a 2,700-km pipeline would be of great benefit for the energy sectors of both the United States and Canada. The project was put on hold in 2011, when environmental groups opposed the fact that the proposed route was supposed to go through an environmentally sensitive part of Nebraska.

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President Obama blocked the pipeline project in January 2012, explaining that the environmental issues regarding Nebraska have not been resolved. As a result, TransCanada drew up new plans and submitted another application last spring. Despite being urged by the bipartisan group of senators, the State Department has announced that the full review of the pipeline project is not expected to be completed before the end of March.

The topic remains highly sensitive, as on the one hand there are the industry representatives and senators who see the pipeline as a means for achieving economic growth, but on the other hand, a number of Democrats and various environmental groups see the potential approval of the project as a compromise with Obama's pledge in his inaugural speech to address global warming.

The Keystone XL pipeline would cross the U.S. border and carry oil through Montana, South Dakota, Nebraska, Kansas and Oklahoma. Opponents of the project have claimed that the process is heat-intensive and uses more energy than traditional oil, thus producing more heat-trapping gases and contributing to global warming. Environmental groups have also pointed out that there is a risk of a potential spill that could be very dangerous.