The Environmental Protection Agency objected Monday to the State Department’s latest review of the Keystone XL oil pipeline, suggesting that more work must be done before the Obama administration can determine whether to approve the 1,179-mile northern leg of the project.

The EPA recommended that State reassess the amount of greenhouse gas that would be emitted by the development of oil sands in Alberta, Canada, as a result of construction of the pipeline, which eventually could transport as much as 830,000 barrels of diluted bitumen crude to refineries in Texas.

Cynthia Giles, assistant administrator in the EPA’s Office of Enforcement and Compliance Assurance, suggested the total gas released could be higher than State has estimated, depending on assumptions in the analysis.

She recommended that State acknowledge that large portions of the crude will sink if there is a spill into a waterway and spell out how it would require pipeline operator TransCanada to respond. She asked State to take another look at an alternative route for the proposed $5.3 billion pipeline, one that would take it away from the Ogallala aquifer, one of the world’s largest sources of fresh groundwater.

The EPA’s objection provides opponents with political ammunition and could force President Obama to weigh in on the permitting decision. Secretary of State John F. Kerry will decide whether the pipeline is in the U.S. national interest unless another federal agency objects. If the EPA continues to challenge State’s analysis, Obama will have to make the call.

In this photo made on March 11, 2013, a wooden stick with a pink ribbon marks the proposed route of the Keystone XL pipeline through farmland near Bradshaw, Neb. (Nati Harnik/AP)

The EPA sharply criticized a draft environmental analysis issued by State in April 2010.

Anthony Swift, an attorney for the Natural Resources Defense Council, said in a statement that “the EPA has got it exactly right — the State Department’s draft environmental review of the Keystone XL tar sands pipeline is insufficient. The EPA determined that the Keystone XL pipeline would have significant negative environmental impacts.”

State Department deputy spokesman Patrick Ventrell said the department “has always anticipated” that in preparing a final supplemental review it would conduct additional analysis and incorporate public comments received on the draft review.