Britain raised its terrorism threat level to “severe” Friday - meaning that an attack is "highly likely" - as Prime Minister David Cameron warned that ISIS poses a "greater and deeper threat to our security than we have known before."
Cameron said he planned new laws to make it harder for Britons to travel to Syria and Iraq to fight alongside Islamist extremists, and said the problem posed by jihadis would last "years, and probably decades."
The country's Home Office said there was no specific intelligence to suggest a terror atrocity was imminent. The U.K.'s biggest police force, London's Metropolitan Police, said it was stepping up visible patrols but no other impact was expected. Cameron said British people should "continue to go about our lives in the normal way."
It is the second time since the discovery of the 2006 transatlantic airliner liquid bomb plot that the U.K. threat level has been higher than "substantial." "This means a terrorist attack is highly likely, although there is no intelligence to suggest that one is imminent," a Home Office statement said.
In response to the British move, U.S. Secretary of Homeland Security Jeh Johnson said American intelligence officials were "unaware of any specific, credible threat to the U.S. homeland" from ISIS. Johnson noted that DHS has already taken steps to enhance aviation security at overseas airports with direct flights to the United States.
"At the same time," Johnson said in a statement, "the Department of Homeland Security is mindful of the potential for homegrown violent extremism inspired by radical ideology overseas, and, both through law enforcement and community outreach, we are taking steps to counter that potential threat."