U.S. actor Sylvester Stallone (L) and California Governor Arnold Schwarzenegger wait for the start of the WBC Heavyweight Championship boxing bout between Vitali Klitschko of Ukraine and Cristobal Arreola of the U.S. at the Staples Center in Los Angeles, California September 26, 2009.[Photo/Agencies]

Sylvester Stallone, Arnold Schwarzenegger and their fellow aging action heroes are back in fighting form for new movie "The Expendables 2," thrilling crowds at the giant Comic-Con pop culture event with footage from the upcoming film.

The new movie, a sequel to 2010's surprise hit about a group of rebel mercenaries out to kill a brutal military leader, appeared similar to the first one in film clips shown Thursday with an emphasis on old-school shootouts over sci-fi fantasy.

"Rambo" and "Rocky" actor Stallone, 66, introduced Schwarzenegger, 64, the former governor of California and star of the "Terminator" movies, to the Comic-Con crowd as "one of my fellow brothers in the hard art business ... a true one-of-a-kind movie star, the likes of whom we'll never see again."

"The Expendables" hit theaters in August 2010 with a tale of aging mercenaries on a new assignment and was positioned as a return to classic 1980s action and adventure versus the Spider-Man and Batman film franchises that rule box offices today.

The film was loaded with older actions stars such as Bruce Willis, and the formula worked well as the movie blasted its way to nearly $275 million at worldwide box offices.

For the sequel, in theaters on August 17, Stallone and Schwarzenegger reunite with Willis, Chuck Norris, Jet-Li, Jason Statham and others.

"The first one was more searching for what was going to work. Is it more dramatic, comedic? But on the second one, you find out what works from the first one, and you try to amplify it," Stallone told the Comic-Con crowd.

"You have the same playbook ... if you have it all together, the second one can surpass the first one, and I think we achieved that."

For the second film, Hollywood's old action heroes set out on another dangerous assignment where Stallone said the Expendables were pushed to the extreme. Film clips showed them in explosive situations, slick fight scenes and trading tough-guy comments with each other.

Stallone said recent Hollywood heroes were "a different kind of action star, more futuristic, scientific, technical. (They) don't have to spend their life pumping iron."

He added that the newer heroes were still valid for their age group, as "each generation has to create their own heroes and each generation redefines the heroes they like to adore."

Much of the audience was filled with fans who have grown up idolizing the old-school heroes including Stallone and Schwarzenegger, and the actors thanked them for their loyalty and dedication.

"The action genre is like a religion, you get your beliefs from these movies, you get your right and wrong from these movies, you get your inspiration," said another of the film's stars, Terry Crews.

Following the panel, Schwarzenegger was given an award from Comic-Con for his contributions and achievements to the film arts and pop culture.