UK authorities raised the level of terrorism threat from “substantial” to “severe” first since July 2009.

The decision was made based on the recommendation of Joint Terrorism Analysis Centre (JTAC), BBC reports.

The Home Secretary Alan Johnson says these measures are not directly linked with recent Detroit events when a terrorist tried to blow up the aircraft, British Guardian reports. However, the official called on British citizens to remain vigilant and assist the police in every possible way.

“Sever” is the fourth level in a five-level scale and it means terrorist attack is considered to be highly likely.

A.G.