Pressure for US President Barack Obama to approve a pipeline to carry crude oil from Canada's oil sands to the US Gulf coast has increased after a State Department report played down the impact it would have on climate change.
But the White House signalled that a decision on an application by TransCanada Corp to build the US$5.4 billion Keystone XL pipeline would be made "only after careful consideration" of the report, along with comments from the public and other government agencies.
"The Final Supplemental Environmental Impact Statement includes a range of estimates of the project's climate impacts, and that information will now need to be closely evaluated by Secretary [of State John] Kerry and other relevant agency heads in the weeks ahead," White House spokesman Matt Lehrich said.
Proponents of the pipeline had earlier crowed about how the State Department report cleared the way for Obama to greenlight the project.
The agency made no explicit recommendation. But the State Department said blocking Keystone XL - or any pipeline - would do little to slow the expansion of Canada's vast oil sands, maintaining the central finding of a preliminary study issued last year.
The 11-volume report's publication opened a new and potentially final stage of an approval process that has dragged for more than five years, taking on enormous political significance.
With another three-month review process ahead and no firm deadline for a decision on the 1,898-kilometre line, the issue threatens to drag into the congressional midterm elections in November.
Obama is under pressure from several vulnerable Democratic senators who favour the pipeline and face re-election.
Canada's oil sands are the world's third-largest crude oil reserve. The oil sands, in Alberta, contain more than 170 billion barrels of bitumen, a tar-like form of crude that requires more energy to extract than conventional oil.
Obama said in June he believed the pipeline should go ahead "only if this project does not significantly exacerbate the problem of carbon pollution".