Federal grand jury looks into violent pipeline protest clash

A federal grand jury in North Dakota is looking into a violent November clash between Dakota Access pipeline opponents and officers in which one woman was seriously injured.

Attorney Ralph Hurvitz says pipeline opponent Steve Martinez has been ordered to testify regarding New York resident Sophia Wilansky's arm injury due to an explosion.

Protesters say she was injured by a grenade thrown by police, while authorities say she was hurt by a small propane tank that protesters rigged to explode.

Martinez, who is from Williston, North Dakota, says he'll refuse to testify and is prepared to be arrested.

Grand jury proceedings are closed to the public. U.S. Attorney Chris Myers declined comment.

Pipeline opponents worry the four-state, $3.8 billion project will harm the environment. The pipeline developer disputes that.