Emmy award-winning US actor James Gandolfini, the star of the long-running mafia drama "The Sopranos," has died at the age of 51 in Italy, media reports said Wednesday.

Gandolfini, who won three Emmys and a Golden Globe for his portrayal of mob boss Tony Soprano on the hit HBO series, suffered a heart attack, celebrity website TMZ and industry daily Variety reported.

Tributes poured in from fellow actors including Susan Sarandon, who tweeted: "So sad to lose James Gandolfini. One of the sweetest, funniest, most generous actors I've ever worked with. Sending prayers to his family."

"I'm truly heartbroken to hear that James Gandolfini has passed away. He is one of my all time favorite actors. Tragic loss," Jonah Hill wrote on the microblogging site, while Steve Carrell said it was "unbelievably sad news."

Gandolfini's agents and HBO were not immediately available to confirm the reports.

TMZ said Gandolfini was in Italy for the Taormina Film Fest in Sicily, where he was expected to participate in a roundtable discussion with Italian director Gabriele Muccino this weekend.

Gandolfini had a long film and stage career before lending his heavy stature and big grin to play a depressed mafioso in "The Sopranos," a celebrated series that ran from 1999 to 2007.

The New Jersey-born actor began acting in the New York theater, making his Broadway debut in the 1992 revival of "A Streetcar Named Desire" with Jessica Lange and Alec Baldwin.

His breakthrough role came as a hitman in Tony Scott's 1993 "True Romance," which he followed with "She's So Lovely" (1997), "8MM" (1999), "The Mexican" (2001), "The Man Who Wasn't There" (2001) and "In the Loop" (2009).

He played CIA director Leon Panetta in last year's Oscar-winning Osama bin Laden manhunt movie "Zero Dark Thirty," and was seen in this year's comedy "The Incredible Burt Wonderstone."

He is survived by his wife, Deborah Lin, whom he married in 2008. He had a son, Michael, with his first wife, Marcy Wudarski.