North Dakota Highway Patrol said it locked the state capitol building in Bismarck on Nov. 14 after more than 500 Dakota Access Pipeline (DAPL) protesters tried to gain entry to the building.

Officials put the capitol in a "soft lockdown," in which all doors were locked and guarded, at 11:30 a.m. CST, said Lieutenant Tom Iverson, spokesman for the highway patrol.

Employees were given the option of going home and were told they could return only with key cards, Iverson said, adding that more than 30 North Dakota Highway Patrol officers were deployed to the building.

The rare security step at the state government headquarters comes as tensions increase over the proposed 1,172-mile, or 1,885 kilometer (km) pipeline.

The state highway patrol received word around 10:30 a.m. CST of a convoy of 140 vehicles driving north toward Bismarck. The convoy entered the capitol grounds after it arrived in the city, Iverson said.

The protesters lacked a permit, required by state law for people to assemble inside the capitol.

There were no arrests or physical altercations, and a few hours later the protesters marched toward the federal courthouse elsewhere in the city, Iverson said.

However, the demonstrators broke into smaller groups and attempted to gain entry to the capitol through various side entrances, he said. "It makes numerous state employees nervous for their safety. That's something these protesters don't think of."

Representatives for the protesters were not immediately available for comment.

In a separate news article, Reuters reported Nov. 14 that the federal government delayed a decision to grant an easement to DAPL's Texas-based owner, Energy Transfer Partners LP, for construction of a segment of DAPL, according to a joint notice published by the U.S. Army and the U.S. Department of the Interior.

The $3.7 billion Dakota Access construction project has drawn steady opposition since summer 2015 from Native American and environmental activists who claim it could pollute nearby water supplies and destroy historical sites.

Those protesters were a factor in the Obama administration's decision to delay the line's completion in September and ask for further review from the U.S. Army.

Other Protests

Previous demonstrations, which have drawn celebrities including actors Shailene Woodley and Susan Sarandon, have occasionally turned violent.

Recently, demonstrators near sacred tribal lands briefly blocked two entrances to a work yard.

Separately, protesters said a woman was struck by a truck driver who drove over her feet and fired shots in the air. There have also been instances of security dogs attacking activists.

Completion of the pipeline, set to run from North Dakota to Illinois, was delayed in September so federal authorities could re-examine permits required by the Army Corps of Engineers.

Plans called for the pipeline to pass under Lake Oahe, a federally owned water source, and to skirt the Standing Rock Sioux Reservation by about one half-mile, or 1 km. Most of the construction has otherwise been completed.