British Home Secretary Theresa May said Friday the country’s terror threat risk level was being raised to “severe,” meaning an attack is “highly likely.”

“The increase in the threat level is related to developments in Syria and Iraq where terrorist groups are planning attacks against the West,” May said.

The threat level is now at the second highest level out of five possible categories and the highest since July 2011.

May said the decision by the Joint Terrorism Analysis Center is made on the basis of intelligence and is independent of government.

Britain has repeatedly expressed concern about British nationals traveling to the Middle East and returning to wage attacks in the UK.