Britain's government has raised the country's terror threat level to "severe," Home Secretary Theresa May said Friday.

It's the fourth-highest of five potential threat levels. According to the U.K. government, it means an attack is "highly likely." But there is no intelligence to suggest an attack is imminent.

May said the threat level was raised because of the risk from the deterorating situation in Iraq and Syria, where extremist militants from the group calling itself the Islamic State (also ISIS or ISIL). May said, however, that there was no specific threat to Britain that caused the raise in the terror level. This is the first time Britain's terror threat level has been at "severe" since 2011.

"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 traveled there from the UK and Europe to take part in those conflicts," May said in a statement. More