YouTube has removed thousands of videos of the radical Yemeni-American cleric Anwar al-Awlaki in a significant step up for the site’s anti-extremism campaign.

It is the first time Google’s video site has taken such concerted action against a particular individual.

The preacher was killed in 2011 by a US drone strike in Yemen, leaving behind a substantial library of sermons, lectures and essays. Awlaki recorded his most radical sermons that explicitly call for violence against the US later in his life, but many, such as a lengthy series on the life of the prophet Muhammad recorded while he was still an imam in the US, are fairly mainstream.

That breadth of material has left Awlaki’s work in a grey area for YouTube. The site’s anti-extremism policy explicitly prohibits videos that incite terrorism or violence, and it also bans individuals named on terror lists from having their own accounts on the site. But the policy doesn’t cover what to do in the event that a person’s work runs the gamut from clearly infringing to apparently innocent, and is uploaded by others.

Now, Google has decided that Awlaki’s entire body of work represents an exception to the rule. According to the New York Times, a search for Awlaki last autumn returned around 70,000 videos. The same search today returns less than 20,000, the vast majority of which are videos about Awlaki, rather than authored by him.

Adam Hadley, the project director of Tech Against Terrorism, welcomed the removal of the videos, but noted that Awlaki’s status as a terrorist on the UN sanctions list should be the key motivator.

“What we’re trying to do is promote greater coherence about how to deal with individuals. Awlaki is a sanctioned individual, and that makes all the difference,” Hadley said. “We can’t have ad-hoc pressure. There needs to be a balanced response on all types of terrorism – we need to remember far-right extremism too – and this is why we need more international co-ordination on defining terror groups.”

Facebook Twitter Pinterest Google’s decision was guided by calls from anti-terror experts to be more proactive about preventing radicalisation, both on- and offline. Photograph: Lionel Bonaventure/AFP/Getty Images

Google’s decision was guided by calls from anti-terror experts to be more proactive about preventing radicalisation, both on- and offline. The issue is that clerics such as Awlaki have large bodies of material that doesn’t cross the line into inciting violence, but hints at the concept. People who watch those videos and agree with their message may then be motivated to seek out the more explicitly hateful videos which have been banned on YouTube for years, but which remain easy to find elsewhere on the internet.

Hadley said: “It’s easy to scapegoat particular videos and shy away from more fundamental questions about how radicalisation works. We’re talking about individuals who are highly vulnerable. This content enables radicalisation, but it’s not the sole problem.”

Born in New Mexico to Yemeni parents, Awlaki was known as the “YouTube Islamist” by 2010, when his militant sermons had been cited by self-radicalised extremists such as Faisal Shahzad, who tried to bomb Times Square in New York, and Roshonara Choudhry, who stabbed Stephen Timms MP because he voted for the war in Iraq.

YouTube has long faced calls to clamp down on Awlaki’s preaching as a result. By 2011, it had implemented its policy of removing hate speech and incitement to commit violent acts, removing a few hundred Awlaki videos in the process. But it allowed the bulk of his output to remain available, arguing at the time it would “continue to remove all content that incites violence according to our policies. Material of a purely religious nature will remain on the site.”

Awlaki’s killing in 2011 was controversial: he was the first US citizen to be a legal target for assassination in the post-9/11 years. He and another US citizen, Samir Khan, the editor of Al Qaeda’s online magazine, were attacked with a US drone. The US later justified the killing as “self defence”.

YouTube declined to comment for this story.