The Keystone Pipeline in the US has been closed after a 210,000-gallon oil leak.
Pipeline operator TransCanada said the incident occurred in a sparsely populated area of Marshall County, South Dakota.
It was then shut off between Canada’s Alberta and Oklahoma and Illinois in the US.
The southern leg of the system, stretching to the Mississippi Gulf Coast, remains open.
The volume of leaked oil has been estimated at 5,000 barrels but TransCanada claims it has been contained to an agricultural area and has not reached any bodies of water.
The leak comes days before a vote on whether to approve a 275-mile-long extension of the project.
A spokesperson for TransCanada added: “We safely shut down the Keystone pipeline after we detected a pressure drop in our operating system resulting from an oil leak that is under investigation.
“The safety of the public and environment are our top priorities and we will continue to provide updates as they become available.”