A malfunction and spill have forced the closure of a major pipeline that carries about 450,000 barrels of oil per day from Canada into the United States. 

TransCanada Corp. says it shut off its Keystone line early Saturday morning after something went wrong with a valve at a pumping station near Milnor, N.D.

newchart

TransCanada 3-month chart

Terry Cunha, a company spokesman, says about 500 barrels of oil spilled in the remote area and crews are cleaning it up and making repairs.

Cunha says TranCanada hopes to resume oil shipments through the line by the end of the week and make good on its commitments to customers by the end of the month.

He says the problem was in a valve located above ground and not in the underground pipeline.

Environmentalists say the spill unscores safety concerns about TransCanada's proposal to extend the Keystone pipeline to carry more oilsands crude into the U.S.