KERPEN, Germany (AP) — Authorities in western Germany have moved to remove tree houses built by activists in an ancient forest slated to be cleared to allow for coal strip mining.

Police in riot gear stood by Thursday as preparations began to remove the roughly 60 treehouses occupied by environmentalists trying to stop the logging from starting next month.

Authorities say the houses pose a fire hazard, which activists reject as "ridiculous." Police used megaphones to warn the activists to leave the hastily cobbled-together tree dwellings, or face being forcibly removed. The number of environmentalists isn't clear.

Power company RWE wants to start cutting down half the forest next month to expand a lignite strip mine.

Last week, workers cleared obstacles placed by protesters from the floor of the Hambach forest, southwest of Cologne.