"If we are going to get serious about climate change, opening the spigot to a pipeline that will export up to 830,000 barrels of the dirtiest oil on the planet to foreign markets stands as a bad idea," said Anthony Swift of the Natural Resources Defense Council.
Republicans and many business groups say the pipeline project would help achieve energy independence.
The State Department, which has federal jurisdiction over the $7 billion pipeline because it begins in Canada, said Tuesday that it would not be able to conclude its review during the first quarter of the year.
White House officials sought to look beyond Keystone, with aides saying Tuesday that the president may also pursue executive actions to fulfill his pledge to tackle climate change.
Associated Press writers Matthew Daly, Josh Lederman and Donna Cassata contributed to this report.
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