Actor James Gandolfini is congratulated for winning the award for best male actor in a drama series for "The Sopranos" at the 14th annual Screen Actors Guild Awards in Los Angeles in this January 27, 2008 file photo. [Photo/Agencies]

LOS ANGELES  - James Gandolfini, the burly actor best known for his Emmy-winning portrayal of a conflicted New Jersey mob boss in the acclaimed HBO cable television series "The Sopranos," has died while vacationing in Rome, Italy, the network said on Wednesday.

Gandolfini, 51, who began his career in live theater in New York, died of a possible heart attack, HBO spokeswoman Mara Mikialian told Reuters.

Since "The Sopranos" ended its run in 2007, Gandolfini has appeared in a number of big-screen roles, including the espionage thriller "Zero Dark Thirty" and the comedy "The Incredible Burt Wonderstone."

At the time of his death, Gandolfini had been working on an upcoming new HBO series titled "Criminal Justice."