JOHN DAY, Ore. — Ammon Bundy, the leader of an armed seizing of a federal wildlife refuge in rural eastern Oregon, was arrested and one person was killed Tuesday afternoon in a traffic stop in rural Oregon, the F.B.I. and the Oregon State Police said.

Seven other people, including Mr. Bundy’s brother Ryan Bundy, were arrested, the authorities said. Another person was hospitalized with injuries that were not life-threatening.

The authorities did not identify the man who was killed, but a member of the Nevada State Assembly, Michele Fiore, who has been a supporter of the Bundy family, said on Twitter that it was LaVoy Finicum. Mr. Finicum had become a de facto spokesman for the occupiers.