Federal regulators have ordered Exxon Mobil to make safety improvements to the ruptured pipeline that spilled an estimated 1,000 barrels of crude oil into the Yellowstone River in Montana.

Transportation Secretary Ray LaHood said Tuesday that "when companies are not living up to our safety standards, we will take action."

Regulators also ordered the company to re-bury the 20-year-old pipeline to protect against external damage and assess risk where it crosses a waterway. They also say the company must submit a restart plan before oil can flow in the Silvertip pipeline again.

Exxon has said the pipeline was 5 to 8 feet below the bottom of the river and that they were considering burying the line deeper when it is repaired.

The cause of the rupture Friday is under investigation, but some officials have speculated that high water levels scoured the river bottom and exposed the pipe to damaging debris.

Mont. Gov. Brian Schweitzer has ordered a review of pipelines that cross rivers in the state.

Officials will look at the pipes' age, location of shutoff valves and whether they are similar to the ruptured pipe.

Associated Press