Firemen extinguish the fire in Prato, Italy, Dec. 1, 2013. (Xinhua/Alberto Lingria)

ROME, Aug. 7 (Xinhua) -- Italian state police said Monday they arrested the leader of a volunteer firefighter unit on suspicion of arson.

The 15-man unit is under investigation for fraud against the state and arson, police said in a statement.

Investigators in the operation believe the unit set trash containers and properties alight, then simulated calls to emergency services in order to get called out to the scene.

The operation was sparked by a tip from the firefighting command based in the Sicilian city of Ragusa, which noticed the suspects' unit was getting called out to emergencies three times as often as the other units.

"They know everything; they know we set the fires," one of the suspects told another in a wiretapped conversation posted on the state police website.

The investigation concerns incidents that took place in 2013-2015. Investigators believe the unit engaged in the fraud and arson in order to earn money.

Volunteer firefighters are paid 10 euros (11.7 U.S. dollars) an hour, but only when they are in action, the police statement said.

Italy this summer has been plagued with scorching temperatures, drought, and devastating wildfires that have destroyed thousands of hectares of public land, including national parks and nature reserves.