Britain raised its terror threat level to "severe" on Tuesday, its second-highest level, following recent attacks in Austria and France.

The threat level of severe means an attack in the United Kingdom is considered highly likely. The level had previously been at "substantial", meaning an attack is thought to be likely.

The decision announced by Home Secretary Priti Patel came after a man who had previously tried to join the Islamic State group stormed through the center of the Austrian capital of Vienna armed with an automatic rifle Monday night, killing four people before police shot and killed him.

Read more: NBC News