LAS VEGAS - Firefighters say a two-alarm fire at a partially constructed medical office building over the weekend in northwest Las Vegas was intentionally set.

Las Vegas fire spokesman Tim Szymanski (zim-ANN'-skee) says people in a nearby business saw children throwing rocks at windows while smoke came from the two-story building before firefighters arrived a little before 11 a.m. Saturday.

Firefighters quickly doused burning trash and construction materials on the first floor of the building.

Szymanski says the building wasn't secured to keep people out, and fire alarms and sprinklers weren't operational.

He says fire investigators found evidence of previous fires.

Police weren't immediately able to find the vandals, but Szymanski says the investigation is continuing.

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