The massacre of 26 people, mostly young children, at a US school has revived the perennial debate about the impact of violent videogames on the warped minds of gunmen behind such tragedies.

Experts are divided over whether games with names like "Assassin's Creed," "Thrill Kill" or "Manhunt - Executions" are blueprints for real-life violent behavior or harmless fantasies that allow young men to vent testosterone.

Some politicians have highlighted the role of violence in television, movies and videogames -- including Colorado governor John Hickenlooper, after 12 people were killed in a movie theater massacre near Denver in July.

"There might well be some direct connection between people who have some mental instability and when they go over the edge -- they transport themselves, they become part of one of those video games," he told CNN.

Senator Jay Rockefeller called the latest massacre a "wake-up call" for federal action. "While we don't know if such images impacted the killer in Newtown, the issue of violent content is serious and must be addressed.

"As parents, research confirms what we already know -- these violent images have a negative impact on our children's well-being," he said, adding: "I'm pushing for that action now before we have to mourn more innocent lives lost."

Adam Lanza, the 20-year-old who killed himself after massacring 26 people, including 20 children, at Sandy Hook Elementary School in Newtown, Connecticut, was reportedly a fan of violent videogames, including "Dynasty Warriors."

California banned the sale of violent videogames to minors, but the US Supreme Court struck down the law in June 2011, saying it violated the right to free speech, enshrined in the First Amendment of the US constitution.

Experts and games developers say the evidence about such games' impact on players is mixed.

"I'm rather tired of this argument. I'm sure you can find a study or two to support the claim that videogames foster violence, but I'm sure you can also find studies that deny it," said specialist and game designer Greg Costikyan.

"In general, my impression is that the idea that media of any sort cause anything other than short-term and minor changes in proclivities to violent behavior has been thoroughly debunked."

But Brad Bushman, a professor of psychology at Ohio State University and co-author of a study published in the Journal of Experimental Social Psychology last month, said players grow more aggressive the longer they play such games.

Of experts who disagree, he said: "It's like global warming. Ninety-five percent of scientists say that global warming is occurring, but you can always find a few scientists saying it's not occurring.

"The same is true. I would say 95 percent of scientists believe that violent media, TV programs, movies, videogames, increase aggression, and only 5 percent or even less believes they have no effect.

"They are outliers, they're not the norm."

Blood-drenched videogames may well have a more harmful effect than violence in movies or TV shows, he told AFP.

When you're playing a videogame, "you're active. You're not just sitting on a couch watching other people. You are actively involved and people learn when they're actively involved.

"You're directly rewarded in a videogame for behaving aggressively... And you get to advance in the game. If you kill people you get points," he said.

But violent videogames do not by themselves create crazed killers.

"Shootings like the one in Connecticut are very rare and you cannot predict them," Bushman said. "But violent videogames increase behavior that's not so rare, like yelling, hitting, pushing, and being an aggressive driver.

"Maybe if you play violent videogames you won't kill somebody, but how do you treat your friends, how do you treat strangers? There's never one cause. Violent video games are maybe one factor."

Nevertheless, Rockefeller, chairman of the Commerce, Science and Transportation Committee, said the Newtown massacre must spark not just debate, but action.

"It would be a travesty if we only looked at Friday's attack -- as well as the many other senseless tragedies we've seen -- in silence and refuse to act," he said.