And that, he said, means more than just "hammering" ISIS in Iraq and helping the U.S. in Syria.
In addition, "we've got to fight radicalization at home," he said during an interview on NBC. "We've got to stop the jihadi terrorists from traveling from our country. We've got to confiscate passports. We've got to make sure we speak up for moderate Islamic voices.
"All of these things need to to be done to help keep our world safe," he said.
The remarks offer a preview of a speech Cameron will give on Monday, in which he will describe the government's plan to fight terrorism over the next five years.
'Sick and brutal reality'
In that speech, he is expected to say that British values are the country's "strongest weapon" against the narrative of Islamic extremists.
"Any strategy to defeat extremism must confront, head on, the extreme ideology that underpins it," he will say, according to his office. "We must take its component parts to pieces -- the cultish worldview, the conspiracy theories, and yes, the so-called glamorous parts of it too."
And he said young people must be disabused of their misconceptions about ISIS.
"If you are a boy, they will brainwash you, strap bombs to your body and blow you up," he plans to say. "If you are a girl, they will enslave and abuse you.
"That is the sick and brutal reality of ISIL."
ISIL is another acronym for the self-proclaimed Islamic State terror group.