The armed activists occupying a national wildlife refuge in southeastern Oregon clashed with environmentalists Saturday as a standoff stretched into a 15th day.

The Oregonian reports (http://goo.gl/yHnphm ) that a shouting match erupted as members of the Center for Biological Diversity, a nonprofit environmental group, tried to speak at a news briefing.

The center's executive director Kierán Suckling tried to speak but the activists screamed and booed him.

Suckling says his group had a more civil interaction with other occupiers afterward. He says it was important to be present and to not criticize the occupation from the sidelines.

The armed group took over the Malheur National Wildlife Refuge on Jan. 2 to protest federal land use policies. So far, authorities have not tried to remove the group from refuge.