BISMARCK, N.D. — The operator of the Keystone oil pipeline restarted the system Monday after a spill onto farmland in North Dakota last week shut down the line.

South Bow said it was watching inclement weather conditions before beginning “a carefully controlled restart” that will include 24/7 monitoring, reduced operating pressures, cleanup of the site and compliance with federal regulators’ requirements.

The federal Pipeline and Hazardous Materials Safety Administration said South Bow restarted the pipeline at a reduced pressure.

The failed section was dug out and replaced and will be taken to a metallurgical lab in Houston for testing, while the repaired pipeline will be tested at different pressures to ensure its integrity, the safety administration said.

The agency’s investigation is ongoing. It is unclear what caused the spill.

The company said it has finished all repairs, inspections and testing at the spill site. The safety administration said it signed off on the company’s restart plan.

— The Associated Press