Ranchers and Native American leaders marched last weekend along the National Mall in Washington DC to protest the controversial pipeline.
White House spokesman Jay Carney said a Nebraska court decision challenging Gov. Dave Heineman's authority over the route through his state meant more time was needed to issue the necessary permit to build the cross-border pipeline.
The American Petroleum Institute, the energy industry's lobby, said last week support was growing for the pipeline.
Oglala Sioux Tribal President Bryan Brewer called on the U.S. government to reject the pipeline.
"Keystone XL is a death warrant for our people," he said Saturday.
Tribal nations have said building the pipeline through Northern Plains states may violate treaties from the late 1800s.
Supporters of Keystone XL say it will help protect the North American energy sector for overseas shocks, though opponents say the more viscous form of Canadian crude oil designated for the pipeline presents a grave risk to the environment.