Authorities say a wildfire that forced the evacuation of some 2,000 people from residential areas just west of Madrid was likely started by several people working together.
Regional justice department chief Regina Planol told Cadena SER radio that the fire affecting three towns was started in six points almost simultaneously, indicating it was arson.
She compared it to "environmental terrorism."
Spanish National Television said some 20 square kilometers (8 square miles) of land have burned.
Alvaro Santamaria, mayor of one of the affected towns, Valdemaqueda, said the fire came as close as 100 meters to the town's houses. He said firefighters were confident the blaze could be brought under control Tuesday.
Spain has seen 1,500 square kilometers (580 square miles) of land burnt in nearly 12,000 wildfires this year.