BENI, Democratic Republic of Congo (Reuters) - Gunmen killed two rangers in Congo's Virunga National Park on Sunday, the Congo Institute for Nature Conservation (ICCN) said in a statement, the second attack this month in the country's restive east.

The attack took place near Rwindi in North Kivu province, north of another attack on May 18 in which three rangers and a worker were killed.

Fighters from the Mai Mai militia were likely to blame, the ICCN said, based on its sources. Reuters was unable to confirm this and the Mai Mai could not be reached for comment.

The Mai Mai comprise several armed bands that formed to resist two invasions by Rwandan forces in the late 1990s. They have since morphed into a variety of ethnic-based militia, smuggling networks and protection rackets.

Virunga is a vast expanse of deep forests, glaciers and volcanos, with more species of birds, reptiles, and mammals than any other protected area in the world.

It has been caught in the middle of militia activity that has destabilised surrounding regions since civil wars fought around the turn of the century.

The ICCN warned of a resurgence of violence in February after suspected Mai Mai militants killed a ranger in a third attack.

(Reporting by Erikas Mwisi, writing by Edward McAllister; Editing by Bernadette Baum)