"We did three films that stay within the same block of time. We need to move on for artistic reasons and obvious physical reasons," Ford said at a news conference. "I feel fit to continue and bring the same physical action."

"Indiana Jones 4" has been in development for over a decade, but the production has recently gained momentum. Lucas has said he and Spielberg, who would direct, are working on a script, though no details have been disclosed.

Ford played Indiana Jones in 1981's "Raiders of the Lost Ark," 1984's "Temple of Doom" and 1989's "The Last Crusade." In the last film, Jones' father was played by Sean Connery, who Ford said might also appear in the planned fourth feature.

"He's part of the emotional fabric of these films. I think there may be an opportunity, I believe that Sean is still willing and I'd be delighted if he joined us," said Ford.

Connery, who attended the Rome event last week, has said that no offer had been made.

Ford declined to provide details about a shooting schedule or film locations, adding that the directors were not yet finished with the script.

"I think it's a real opportunity to make a film as successful ... as the ones we've made before," he said.