A review of almost a decade of studies has found that exposure to violent video games is a "risk factor" for increased aggression.

A review of almost a decade of studies found that exposure to violent video games was a "risk factor" for increased aggression.

But the same team of experts said there was insufficient evidence to conclude that the influence of games such as Call Of Duty and Grand Theft Auto led to criminal acts.

The findings have prompted a call for more parental control over violent scenes in video games from the American Psychological Association (APA).

"The research demonstrates a consistent relation between violent video game use and increases in aggressive behaviour, aggressive cognitions and aggressive affect, and decreases in pro-social behaviour, empathy and sensitivity to aggression," a report from the APA task force on violent media concludes.

The report said no single influence led a person to act aggressively or violently. Rather, it was an "accumulation of risk factors" that resulted in such behaviour.

The APA has urged game creators to increase levels of parental control over the amount of violence video games contain.

At a meeting in Toronto, Canada, earlier this month the association's ruling council also called for a video game rating system that took more notice of violence, and for games to be more appropriate to players' age and psychological development.

Dr Mark Appelbaum, who chaired the APA task force, said while scientists had investigated the use of violent video games for more than two decades, there is very limited research addressing whether violent video games caused criminal violence.

"However, the link between violence in video games and increased aggression in players is one of the most studied and best established in the field," he said.

"We know that there are numerous risk factors for aggressive behaviour. What researchers need to do now is conduct studies that look at the effects of video game play in people at risk for aggression or violence due to a combination of risk factors."

The task force conducted a comprehensive review of more than 300 violent video game studies published between 2005 and 2013.

The psychologists identified a number of shortcomings in the literature, including a failure to look for differences in the behaviour of boys and girls who play violent video games.

They also criticised a lack of research on the effects of violent video games on children younger than 10, or their impact over the whole course of a child's development.