Obama said congressional Republicans "forced" his decision due to the "arbitrary nature" of the Feb. 21 that was set by a GOP-written provision in a recent tax bill that Obama signed.
Administration officials says the looming deadline cut short the time needed to conduct environmental reviews after the State Department ordered the project developer to find an alternate route to avoid environmentally sensitive areas of Nebraska.
The proposed $7 billion pipeline would carry oil from tar sands in western Canada to refineries in Texas, passing through Montana, South Dakota, Nebraska, Kansas and Oklahoma.
The Associated Press contributed to this report.
