US lawmakers pressed President Barack Obama on Wednesday to green-light the massive US-Canada "Keystone" pipeline that has drawn heavy fire from environmentalists, saying the project will create jobs.

"Your decision is crucial for both American job opportunities and America's energy security," more than two dozen members of the Republican-controlled House Energy and Commerce Committee wrote in a letter to the president.

The lawmakers complained that an "open-ended" US State Department review into a government study on the project's environmental impact could add needless delays, and insisted that "ample analysis" backed going ahead with the pipeline.

"Mr President, each day that you postpone the decision beyond the 90-day interagency comment period (ending November 24) is another day that thousands of Americans remains unemployed while awaiting a job to build the pipeline or refine the product it delivers," they wrote.

The State Department has been holding public consultations on plans to build the 1,700-mile (2,700-kilometer) Keystone XL pipeline from the tar sands of Canada's Alberta province to the Gulf of Mexico in the southern United States.

In its long-awaited environmental impact statement on the project, the State Department said in August that the pipeline would be safer than most current oil transportation systems.

Many environmentalists fear a potential pipeline accident would spell disaster for aquifers in central US Great Plains states. That could disproportionately endanger rural towns and Native Americans, they say.

Friends of the Earth last month alleged that emails it obtained through the Freedom of Information Act showed that department employees held a "pro-pipeline bias and complicit relationships with industry executives."

The State Department denied the charges, saying it had behaved "transparently and evenhandedly" toward the pipeline project.

Washington is considering the permit for the $7 billion project, due to stretch across 1,700 miles (2,700 kilometers), part of the broader $13 billion Keystone pipeline system.