If it's not "solved" by the time he's scheduled to take office in January, the U.S. president-elect vowed quick action on the Dakota Access oil pipeline.

The U.S. Army Corps of Engineers in early December said it would not approve an easement for further construction on the pipeline to bridge Lake Oahe in North Dakota. Jo-Ellen Darcy, an Army assistant secretary for civil works, said the decision stemmed in part from water-quality concerns expressed by the Standing Rock Sioux Tribe in North Dakota.

State regulators and industry leaders say there's not enough pipeline capacity to carry all of the oil produced from the region, leaving rail as the primary alternate transport method. Several derailments of trains carrying oil from North Dakota proved deadly over the past few years.

Donald Trump, who is slated to assume the U.S. presidency in mid-January, told Fox News during the weekend he'd step into the process if it's required.

"Let me not answer the Dakota [oil pipeline question] because perhaps that'll be solved by the time I get there, so I don't have to create enemies on one side or the other," he said. "But I will tell you when I get to office, if it's not solved, I'll have it solved very quickly."

He did not elaborate on what "solved" implied.

Energy Transfer Partners, a company in which Trump once invested, and Sunoco Logistics Partners, the two companies behind the pipeline's construction, said the decision from the Army Corps of Engineers was a delay tactic from President Barack Obama, whose administration ruled against the Keystone XL oil pipeline on environmental grounds.

Pipeline developers are pressing their case in court, pointing to July permits from the Army Corps for construction in the area of concern. According to a report in The Hill, a judge in the District Court for the District of Columbia said additional briefs from both the tribes working to halt construction and the companies behind the projects are due in February.