Canadian Foreign Minister John Baird called Thursday for the United States to finally decide, one way or another, whether it will permit the construction of the Keystone XL oil pipeline.

After years of delay to the pipeline, intended to carry heavy crude from Alberta's oil sands south to Texas refineries, Baird suggested Canada's patience was running thin with its southern neighbor, already the biggest buyer of Canadian oil.

"The time for Keystone is now," he said in a speech to the US Chamber of Commerce in Washington.

"I'll go further -- the time for a decision on Keystone is now, even if it's not the right one. We can't continue in this state of limbo."

US President Barack Obama is expected to decide this year whether to greenlight the $5.3 billion, 1,179-mile (1,897-kilometer) pipeline, first proposed back in 2008.

It was presented by TransCanada, which operates oil and gas pipelines in North America.

Environmentalists have opposed the pipeline because the oil it will carry requires huge amounts of energy and water to extract, and producing and refining it generates a large amount of damaging emissions in the process.

They also warn the pipeline will carry risks of environmentally damaging spills.

But Baird insisted that it "will have no significant environmental impact," citing a study by the US State Department, which is in charge of reviewing the huge project.

In addition, he said, it will replace heavy oil from other suppliers. Without the pipeline, the oil would end up being shipped to the United States by freight train.

"Compared to sending by pipelines, sending by rail results in elevated greenhouse gas emissions and a considerably higher per-mile incident rate," Baird added.

In recent months, there have been at least three major accidents by trains carrying heavy oil produced in North Dakota, including a deadly crash in eastern Canada.

Baird was visiting Washington for a meeting of foreign ministers, and will have a chance Friday to raise the pipeline issue in a meeting with top US diplomat John Kerry.

State Department spokeswoman Jennifer Psaki said the agency was still awaiting the finalization of a key environmental impact review, after giving the public the opportunity to comment on a draft.

"When that's released, obviously, there'll be a time period before a decision is made," Psaki said.

"But this is not a backroom decision made between the United States and the Canadians. There is a process that's in place that takes into account many different factors, and we'll let that process see itself through."

At the White House, spokesman Jay Carney fended off questions on the timeline for a decision, which has placed Obama in a tug of war between environmentalists and business.

"I think that once the process is moving forward, we'll apprise you of that," Carney told journalists.

"And, you know, when a decision is made, we'll announce it."