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PHOENIX (AP) -- Arizona authorities confirmed Thursday that 11 vehicles area have been shot with bullets or other projectiles in the last two weeks, nearly all of them on freeways in the Phoenix area.

The latest confirmed shooting involved a commercial truck whose driver reported a bullet hole in the cargo area Thursday morning. The driver had been making deliveries for hours, and wasn't sure when or where the truck was shot, Arizona Department of Public Safety spokesman Raul Garcia said.

Most of the vehicles hit since the gunfire began on Aug. 29 were traveling on Interstate 10, a main route through central and west Phoenix. No one has been seriously injured, but one bullet shattered a windshield, and broken glass cut a 13-year-old girl.

"Anytime that you have multiple shootings against American citizens on a highway, that's terrorism," Department of Public Safety Director Frank Milstead said. "It's just a matter of time before there is a tragedy."

Authorities also were studying a tractor-trailer rig at a location near I-10 and a car whose window was severely cracked Thursday, but those results weren't conclusive, Garcia said.