Seventeen people have been detained outside North Dakota's state Capitol building in Bismarck over the oil pipeline. The area was placed in lockdown for a short while during the protest, local TV reported.
Police said three protesters had refused orders to leave the governor's residence in the grounds of the Capital building on Thursday. Earlier, 14 people were arrested after staging a sit-in in the wing of the capitol.
The grounds were placed in lockdown due to what police said was "unforeseen protest activity," local TV channel KFYR reported. The TV station reported that several people had attempted to hold talks with state Governor Jack Dalrymple.
Those arrested face charges of criminal trespass after their protest in Bismarck, which took place hours after a march closed the route of the controversial pipeline near the small town of Cannon Ball.
More than 500 clergy from around the world also gathered on Thursday at a campfire at the main protest camp as part of an interfaith prayer day.
Demonstrators once again called for a halt to the construction of the $3.8 billion pipeline that will carry oil from North Dakota to a shipping point in Illinois.
No sign of end to protests
Environmentalists and Native American communities have protested against the pipeline for months, saying it could harm drinking water and construction could damage sacred sites.
Clashes between protesters and police have resulted in more than 400 arrests since August.
The most recent incident took place on Wednesday, when law officers in riot gear used pepper spray to deter dozens of protesters who tried to cross a frigid stream to access property owned by the pipeline developer. Two people were detained.
About 140 people were arrested on the property last week in a law enforcement operation to clear the encampment that protesters had established on the land.
Confusion remains over whether the protests have succeeded in forcing the pipeline to be rerouted.
On Tuesday, US President Barack Obama said the US Army, which owns the land, was mulling alternative routes. But the Texas-based developer Energy Transfer Partners said shortly after it had no plans to change the direction of the pipeline.
mm/kl (AP, Reuters)
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