U.S. federal regulators have ordered the Keystone pipeline to remain shut down until its Canadian owner takes corrective action aimed at determining the cause of a breach that leaked an estimated 1.4 million litres of oil in northeastern North Dakota.

The Pipeline and Hazardous Materials Safety Administration issued the order Tuesday to Calgary-based TC Energy. The action comes one week after the pipeline leak was discovered and affected about 2,090 square metres of land near Edinburg in Walsh County.

The pipeline has been shut down since Oct. 29. It is designed to carry crude oil across Saskatchewan and Manitoba, and through North Dakota, South Dakota, Nebraska, Kansas and Missouri on the way to refineries in Patoka, Ill., and Cushing, Okla.

The order requires the company to send the affected portion of the 76-centimetre steel pipeline to an independent laboratory for testing. The company also must develop a plan to restart the line and for remediation.

TC Energy, formerly known as TransCanada, said in a statement it expects to have the damaged portion of the pipeline excavated by the end of the week.

The company said it has about 200 people at the site working around the clock who are "focused on clean-up and remediation activities."

"We're continuing to monitor air quality around the site and the surrounding area throughout cleanup, with no concerns," TC Energy said.

Karl Rockeman, North Dakota's water quality division director, said Wednesday about 954,000 litres of crude oil have been recovered.

Rockeman said some wetlands were affected, but not any sources of drinking water.

The pipeline spill and shutdown come as the company seeks to build the $8 billion US ($10.5 billion Cdn) Keystone XL pipeline that would carry oilsands oil from Alberta to refineries in Texas. The proposed pipeline has drawn opposition from people who fear it will cause environmental damage.