David Cameron said the Islamic State's actions in Iraq and Syria pose a threat to the UK's security.
The Prime Minister was speaking after the UK's terror threat level was raised from substantial to severe.
"The ambition to create an extremist caliphate in the heart of Iraq and Syria is a threat to our own security here in the UK," David Cameron said.
Mr Cameron warned that the UK could be facing a "terrorist state on the shores of the Mediterranean" if the Islamic State continued to expand its territory.
"The root cause of this threat to our security is quite clear. It is a poisonous ideology of Islamist extremism that is condemned by all faiths and faith leaders."
The PM wants to confiscate passports. But in Cardiff they want to solve extremism at it's roots - they just can't get the help to do it.
David Cameron has unveiled a series of new measures to combat the threat of terrorism.
Rumours suggesting London's Tube network will be targeted in a terrorist attack on Monday are "completely untrue", police say.