Terrorist training videos will be banned from appearing on YouTube, under revised new guidelines being implemented by the popular video-sharing site.
The Google-owned portal will ban footage that advertises terrorism or extremist causes and supporters of the change hope it will blunt al-Qaeda's strong media online campaign.
The move comes after pressure on the internet search engine from Connecticut Senator Joseph Lieberman.
In addition to the ban on terror training videos, the new YouTube guidelines includes bans on videos that incite others to commit violent acts, videos on how to make bombs, and footage of sniper attacks.
The internet has become a powerful tool for terrorism recruitment. What was once conducted at secret training camps in Afghanistan is now available to anyone, anywhere because of the web.
Chatrooms are potent recruitment tools, but counterterrorism officials have found terrorist-sponsored videos are also key parts of al-Qaeda's propaganda machine.
"It's good news if there are less of these on the web," FBI spokesman Richard Kolko said. "But many of these jihadist videos appear on different websites around the world, and any time there is investigative or intelligence value we actively pursue it."
There have been online terror-training videos ranging from how to slit a victim's throat and how to make suicide vests to how to make explosives from homemade ingredients and how to stalk people and ambush them, said Bruce Hoffman, a counterterrorism expert and professor at Georgetown University.
Hoffman said he does not know whether the videos were posted on YouTube, but they have been available at other sites online.
A year ago, a Homeland Security Department intelligence assessment said: "The availability of easily accessible messages with targeted language may speed the radicalisation process in the homeland for those already susceptible to violent extremism."
Recognising the growing threat of radicalisation, Lieberman - the Democrat-turned-independent who chairs the Senate Homeland Security and Governmental Affairs Committee - asked Google to ban videos from al-Qaeda and other Islamist terror groups.
He said the private sector also has a role in protecting the United States from terrorists. By banning these videos on YouTube, "Google will make a singularly important contribution to this important national effort," Lieberman wrote to Google's chairman and chief executive, Eric Schmidt, in May.
Representatives of Google and YouTube would not respond to questions about Lieberman's appeal.
Despite the move there is a debate among radicalisation experts of whether shutting down extremist sites is the most effective way to counter the threat.
They say keeping them online allows analysts and investigators to monitor what is being said and in some cases who is saying it.
"The reality is by shutting it down, it is more or less a game of whack-a-mole: it pops up somewhere else," said Frank Ciluffo, homeland security director at George Washington University.
However, he said, forcing extremists to find other ways to post videos could give officials a better opportunity to monitor them.
