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

Trucks and workers started a cleanup effort at the site of a spill of the Keystone oil pipeline in rural North Dakota

The Keystone Pipeline declared force majeure on scheduled oil shipments after a leak spilled an estimated 3,500 barrels of crude in a North Dakota field.

The Keystone oil pipeline was shut down Tuesday morning after it ruptured in North Dakota, with the spill confined to an agricultural field.

A portion of the Keystone oil pipeline has ruptured, forcing it to be shut down in North Dakota. It is not known what caused the break and the amount of crude oil that flowed into an agricultural field in Fort Ransom,

The latest leak in the Keystone oil pipeline in North Dakota on Tuesday continues the troubled history of the 15-year-old pipeline

According to the North Dakota Department of Environmental Quality, there was a malfunction of the pipeline near Fort Ransom that caused oil to spill into a nearby field south of a pump station. A small stream near the site has been isolated and remains unaffected at this time,

The cause of the leak and the duration of the shutdown are currently unknown. Federal and state agencies will investigate the incident and oversee cleanup. The operator of the Keystone Pipeline that carries oil from Canada into the U.