LONDON (AP) -- Prime Minister David Cameron pledged Friday to plug gaps in Britain's armory to combat terror, describing the extremist threat posed by the Islamic State group as being more dangerous than even that of al-Qaida.
Cameron's remarks came just moments after authorities raised Britain's terror threat level to severe, the second highest level. The decision was related to developments in Iraq and Syria, but there was no information to suggest an attack was imminent.
"What we are facing in Iraq now with ISIL is a greater threat to our security than we have seen before," Cameron said, using an abbreviation for a longer name the Islamic State previously used: the Islamic State of Iraq and Levant.
British Prime Minister David Cameron looks to answer questions from journalists during a media conference in Downing Street, London, Friday Aug. 29, 2014. The Home Secretary Theresa May has announced that UK's terror threat level is being raised from "substantial" to "severe" on Friday, meaning that a terrorist attack is considered highly likely.(AP Photo/Paul Hackett, Pool)
He told reporters that while the Taliban facilitated al-Qaida terrorism, the Islamic State group is "effectively a state run by terrorists." He said the ambition to create an Islamist caliphate is not something that could be ignored.
"We could be facing a terrorist state on the shores of the Mediterranean and bordering a NATO member," he said.
Intelligence and security services now believe some 500 Britons have gone to fight in Syria and potentially Iraq. Some of the plots are likely to involve fighters who have traveled from Britain and Europe to take part in fighting in the Middle East.
British police have appealed to the public to help identify aspiring terrorists after the killing of an American journalist focused attention on extremism in the U.K. The involvement of a person of British nationality in James Foley's beheading underscored the need to identify those who might travel abroad to fight or are at risk of being radicalized.
The attack on a Jewish museum in Brussels also underscored the willingness of the members of the group to attack Europeans.
British authorities say around 70 arrests have been made in the first half of the year for a variety of offenses, including fundraising, preparing for terrorism acts and traveling abroad for terrorist training. The police say such arrests are being made at a rate five times greater than 2013.
One action Cameron outlined was the possibility that passports could be taken away. He said further measures would be described in the House of Commons on Monday.
Britain also wants to revive a directive to enable police and security services to share passenger records in the European Union. Concerns about civil liberties have stalled the measure in the European Parliament.
"The root cause of this threat to our security is quite clear," Cameron said. "It is a poisonous ideology of Islamist extremism that is condemned by all faiths and faith leaders."
Britain raised the country's terror threat level from substantial to severe just before Cameron held his news conference. The threat level means a terrorist attack is considered highly likely.
Home Secretary Theresa May said the decision by the Joint Terrorism Analysis Center was made on the basis of intelligence and independent of the Cameron and his Cabinet. "Severe" is the second-highest of five levels.
The last time the rate was raised to severe was in September 2010 - in response to the attempt to detonate a bomb on a U.S. passenger plane over Detroit. It was last raised to the highest level, or critical, in June 2007, after a car on fire was driven into the Glasgow Airport terminal building and - separately - two devices were found in cars in central London.
On July 7, 2005, four suicide bombers attacked the London transit system at rush hour and killed 52 commuters and injured hundreds.