Energy Transfer Partners, which has been working to finish construction on the 1,170-mile, $3.7 billion pipeline, contends it would be a safer way to transport oil from North Dakota to Illinois. But Native American tribes say it threatens the local water supply, sacred land and tribal burial ground.

David Archambault II, the chairman of the Standing Rock Sioux tribe, said in a statement on Wednesday that the tribe applauded Mr. Obama’s “commitment to protect our sacred lands, our water and the water of 17 million others.”

But he said work on the pipeline should be stopped while the Army Corps examined the issue.

“The nation and the world are watching,” Mr. Archambault said. “The injustices done to Native people in North Dakota and throughout the country must be addressed.”

The number of protesters has grown to several hundred, many drawn from across the country. Last week, the standoff boiled over as officers in riot gear tried to force crowds from protest camps near Cannon Ball. In the monthslong unrest, more than 400 people have been arrested, some accused of engaging in riots and conspiracy to endanger by fire and explosion.