U.S. Secretary of State John Kerry on Thursday urged countries at U.N. climate talks in Lima to move away from using fossil fuels while demonstrators gathered outside the meeting urged him to reject the Keystone oil pipeline.

"Coal and oil may be cheap ways to power an economy today... but I urge nations around the world: Look further down the road," he said.

As Kerry delivered a 30-minute speech trying to inject momentum into difficult UN climate negotiations, environmentalists stood outside holding signs calling on him to urge President Barack Obama to reject the Canada-to-U.S. oil pipeline, which would carry heavy Canadian crude to Texas.

Kerry must make the final recommendation to Obama about whether the $8 billion pipeline that has been delayed more than five years is in the national interest and whether he should approve it.

Neither Obama nor Kerry have said publicly whether they favor approving the pipeline but said they will wait for the Nebraska court ruling.

Environmental activists in Lima said if Kerry approves the project, he would be going against the spirit of his speech.

"Secretary Kerry sure sounded like someone who was gearing up for rejection," said Jamie Henn of green group 350.org. "(He) has left himself no logical option except to recommend President Obama say no to Keystone XL."

The chief negotiator at UN climate talks for the Pacific island nation Nauru said approving Keystone would erode the positive steps the United States has made to show climate leadership.

"Now is not the time to call the superpower's commitment to tackling this crisis into question by letting this dirty, myopic, and irresponsible project go forward," said Nauru Ambassador Marlene Moses.

Canada is under strong economic pressure to send its vast reserves of heavy crude oil to market. But Canadian Environment Minister Leona Aglukkaq told Reuters she has no plans to meet Kerry in Lima.

A Nebraska Supreme Court ruling on whether the proposed route of the pipeline is legal could come as early as Friday. If the court deems the route legal, Obama may be forced to make a decision soon. Final construction could begin with presidential approval.

On any Friday from now until the end of January, the seven-judge panel may issue its ruling on whether state lawmakers were right to clear the way for the controversial project.