PORTLAND, Ore. (AP) — Federal prosecutors say investigators combing through an Oregon wildlife refuge occupied for nearly six weeks by an armed group discovered firearms, explosives and trenches dug near artifacts.

Assistant U.S. Attorneys Ethan Knight and Geoffrey Barrow also said in a court filing Tuesday that the FBI is concerned vehicles at Malheur National Wildlife Refuge might be booby-trapped.

Prosecutors say the occupiers appear to have dug two trenches near "sensitive artifacts." The refuge contains artifacts and burial grounds sacred to the Burns Paiute Tribe.

Investigators also found significant amounts of human feces and spoiled food.

The FBI expects to take three weeks to process the preserve seized by occupiers demanding the government relinquish control of public lands. More than two dozen people were arrested.

Prosecutors provided the information in a response to a motion from defense lawyers who want access to the site.