Russian troops have dug an eight kilometre long canal to keep wildfires away from a nuclear arms site.
Forest and peat fires in Russia, caused by a heatwave, have killed at least 52 people and destroyed thousands of homes.
Smoke from the wildfires has blanketed the capital, Moscow, forcing people to wear surgical masks to filter out the smog.
A Russian radio station says army troops have excavated a canal around the Sarov nuclear arms facility, 350km east of Moscow, which is ringed by forest.
Last week, Russia's nuclear chief assured the government that all explosive and radioactive material had been removed from the site as a precaution.
