The United Kingdom raised its terror threat level from substantial to severe on Friday, meaning the country believes a terrorist attack is “highly likely.” Developments in Syria and Iraq led Britain’s Home Office to raise the threat level, although U.K. intelligence officials didn’t have evidence to suggest an attack is imminent. In response to the raising of the U.K. terror level, the U.S. said the FBI was unaware of any “specific, credible threat to the U.S. homeland from” the Islamic State, or the militant group formerly known as ISIS. 

“The increase in the threat level is related to developments in Syria and Iraq, where terrorist groups are planning attacks against the West. Some of these plots are likely to involve foreign fighters who have travelled there from the U.K. and Europe to take part in those conflicts,” U.K. Home Secretary Theresa May said in a statement. “The first and most important duty of government is the protection of the British people. We have already taken steps to amend our powers and increase our capabilities for dealing with the developing terrorist threats we face. That process will continue and the British public should be in no doubt that we will take the strongest possible action to protect our national security. We face a real and serious threat in the U.K. from international terrorism. I would urge the public to remain vigilant and to report any suspicious activity to the police.”

The change in the threat was based on an assessment by Britain’s Joint Terrorism Analysis Centre.

U.S. Secretary of Homeland Security Jeh Johnson said in a statement that his agency and the FBI don’t know of any threats to America from ISIS. “At present, the U.S. Department of Homeland Security and the FBI are unaware of any specific, credible threat to the U.S. homeland from” ISIS, Johnson said. “Plainly, however, violent extremists who support ISIL have demonstrated the intent and capability to target American citizens overseas, and [ISIS] constitutes an active and serious threat within the region.”