BISMARCK, N.D. — The Keystone oil pipeline was shut down Tuesday morning after it ruptured in North Dakota, halting the flow of thousands of gallons of crude oil from Canada to refineries in the U.S.

Officials say the Keystone oil pipeline has ruptured in North Dakota, with the spill confined to an agricultural field.

The Berkshire Hathaway chair and CEO has taken steps to protect his portfolio from the selloffs now sweeping American and global markets.