The State Department's chief investigator will review the Obama administration's handling of a TransCanada's request to pipe oil from western Canada to Texas, following complaints from 13 Democratic lawmakers and one independent.

Deputy Inspector General Harold W. Geisel said the special review will centre on whether the State Department followed all federal laws and regulations related to the $7 billion Keystone XL project. The 2,736-kilometre pipeline would carry oil derived from tar sands in Alberta, Canada, to refineries in Houston and Port Arthur, Texas.

The pipeline would travel through Montana, South Dakota, Kansas, Nebraska and Oklahoma before reaching Texas.

Geisel's announcement of the review comes one day after thousands of protesters gathered in Lafayette Square across from the White House to oppose the pipeline plan. During Sunday's rally, the crowd linked hands to surround the White House, keeping up pressure on President Barack Obama as his administration decides whether to approve the pipeline project. The State Department has authority over the project because it crosses a U.S. border.

Sen. Bernie Sanders, I-Vt., said Monday that Obama should delay a decision on the pipeline request until the inspector general's investigation is finished. The administration has said it expects to decide by the end of the year, although in recent days officials have hinted that timeline could slip.

"This is a critically important issue for our environment and the energy future of our country," Sanders said. "At a time when all credible scientific evidence and opinion indicate that we are losing the battle against global warming, it is imperative that we have objective environmental assessments of major carbon-dependent energy projects."

Sanders was one of three senators who requested the review, saying they were disturbed by media reports that a company that performed an environmental review on behalf of the State Department had listed pipeline developer TransCanada as a "major client."

Eleven House members — all Democrats — also asked for the IG review.

Conflict of interest questions

In a letter last month, the lawmakers asked the inspector general to look at all contractual or financial relationships between the consultant, Houston-based Cardno Entrix, and TransCanada.

They also asked for a review of State Department emails involving a TransCanada lobbyist who had worked in Secretary of State Hillary Rodham Clinton's 2008 presidential campaign.

Clinton told The Associated Press last month that that she had no reason to believe there was a conflict of interest involving the TransCanada lobbyist, Paul Elliott.

The underground pipeline would carry an estimated 700,000 barrels of oil a day, doubling the capacity of an existing pipeline from Canada.  

Supporters say the line could significantly reduce U.S. dependence on Middle Eastern oil, while opponents say it would bring "dirty oil" that requires huge amounts of energy to extract and could cause an ecological disaster in case of a spill.

Rep. Steve Cohen, D-Tenn., who led the House effort for the IG review, called the allegations against Cardno Entrix and the TransCanada lobbyist "disconcerting," adding that the claims are serious enough to warrant a delay in the State Department's decision whether to approve or reject the pipeline.

Given the significant economic, environmental, and public health implications of the proposed Keystone XL pipeline, the American people deserve an accurate, unbiased review," Cohen said.