North Dakota regulators will review what caused a Mandan natural gas pipeline leak that temporarily left more than 5,000 people without heat, the state Public Service Commission says.

Commissioner Kevin Cramer called the review a standard response to a pipeline failure, and said there was no evidence so far that the leak was caused by violations of pipeline safety rules. The pipe was installed more than 50 years ago.

Al Moch, the commission's pipeline safety director, was present when the leaking pipe was uncovered, Cramer said at a PSC meeting Wednesday. Montana-Dakota Utilities Co. provides natural gas service to Mandan.

"We actually have every indication that there was no violation," Cramer said. "There was no corrosion on the line … There will be a thorough investigation, not only by the Public Service Commission, but by Montana-Dakota Utilities, as is appropriate in a situation like this."

The leak was reported early Sunday morning. Mark Hanson, an MDU spokesman, said service was restored to homes by Tuesday afternoon. Now, the company's attention is focusing on discovering what caused the leak, Hanson said.

The pipeline was lowered recently as part of a nearby road construction project, but that has not been pinpointed as the leak's cause, Hanson said.