NEW YORK (AP) - Former ''Sopranos'' star Michael Imperioli said he was at a loss to guess why someone left a pipe bomb that detonated outside a theater he owns.

New York Police Department spokesman Paul Browne said there had been ''no known threats to the location or its owners'' before the explosion at 1 a.m. Tuesday outside Studio Dante.

Imperioli played Christopher Moltisanti, Tony Soprano's nephew, on the popular HBO television show.

Imperioli told the Daily News he was ''completely baffled'' by the blast, saying he was unaware of any conflicts with the building's tenants or neighbors.

''This whole day felt like a hallucination. It's surreal,'' Imperioli said.

Investigators believe someone planted the device - a fused pipe bomb - on a tiled ledge near the theater entrance before it exploded, Browne said.

The blast blew out the windows of an unoccupied van parked outside Studio Dante, but Mayor Michael Bloomberg said no one was injured. Three residential floors above the theater were evacuated while authorities made sure they were safe.

''While there certainly is no evidence that this was terrorism, we are taking this and every act of violence extremely seriously, and we'll take every step to identify and apprehend whoever set this explosive device off,'' Bloomberg said.

Studio Dante is described on its Web site as ''an unexpected jewel-box that was built to house progressive new plays.'' Imperioli created it with his wife, Victoria.

Though police sometimes recover pipe bombs while making arrests, explosions are rare. One exception came in 2004, when an emotionally disturbed police officer set off a pipe bomb inside a Times Square subway station. He was sentenced to one to three years in prison for reckless endangerment.

In 2005, an explosion caused by two makeshift grenades fitted with fuses blew out a window near Manhattan's British consulate. There were no injuries or arrests.

By TOM HAYS Associated Press Writer

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