Image copyright Reuters Image caption A new pipeline will link Canada to Nebraska and join with existing pipes to go on to Texas

The US state department has raised no major environmental objections to the Keystone XL oil pipeline from Canada, according to a new report.

Environmentalists say the pipeline will lead to increased carbon emissions, contribute to global warming, and risk spills on its route.

President Barack Obama has yet to decide whether he will permit it.

The 1,179-mile (1,897km) pipeline would carry tar sand oil from Alberta in Canada to Nebraska.

The oil would then be transported on existing pipes to refineries in Texas. The southern section of the project was finished last year.

The Keystone XL project aims to carry some 830,000 barrels of heavy crude a day from the fields in Alberta.

Political debate

The US still needs to approve 875 miles of the route across American land.

On Friday, a spokesman said the White House was still awaiting further review from other government agencies and the public.

Analysis The Final Supplemental Environmental Impact Statement is as dry as its name implies. An 11-volume tome which reaches no firm conclusions, it's being seized upon not so much for what it says as for what it doesn't say. With a heavy dose of pragmatism, the report points out that oil reserves in this particular part of northern Alberta are likely to be developed whether the Keystone XL pipeline is approved or not. It makes the point that alternative methods of conveying oil from Canada to America's Gulf coast - for example by rail or barge - would probably have as great an impact on the environment as a pipe beneath the ground. But it doesn't explicitly say that the long-delayed project would lead to an increase in greenhouse gases - and supporters are seizing on that as a sign that the Obama administration will eventually back it, despite the consternation that would cause among environmentalists.

"The president has clearly stated that the project will be in the national interest only if it does not significantly exacerbate the problem of carbon pollution," Matt Lehrich said.

In an environmental impact statement released on Friday, the state department said that approval was "unlikely to significantly impact the rate of extraction in the oil sands or the continued demand for heavy crude oil at refineries in the United States".

The report does not directly recommend approval of the 875-mile section. Rather, it is described as a technical assessment of the project's environmental impact.

The pipeline would be built by TransCanada Corp, which first applied for a permit from the US government in 2008.

TransCanada chief executive Russ Girling said on Friday he was "very pleased" with the report's findings.

The project, estimated at $7bn (£4.26bn), has become a source of significant debate, with environmental groups saying it would contribute to global warming.

The opposition Republicans have long supported the initiative, saying it will boost the US economy, create jobs, and reduce North America's dependence on foreign oil.

"This report from the Obama administration once again confirms that there is no reason for the White House to continue stalling construction of the Keystone XL pipeline," Republican Senate Minority Leader Mitch McConnell said in a statement.

"So, Mr President, no more stalling- no more excuses. Please pick up that pen you've been talking so much about and make this happen. Americans need these jobs."

Environmental groups condemned the report. The National Resources Defense Council said it was "absolutely not in our national interest" to allow its construction.

"Piping the dirtiest oil on the planet through the heart of America would endanger our farms, our communities, our fresh water and our climate," the council's international programme director, Susan Casey-Lefkowitz, said.

Other US agencies, including the Environmental Protection Agency, have 90 days to comment before the state department issues its final recommendation to Mr Obama.