The UK’s terror threat level has been raised from “substantial” to “severe”, home secretary Priti Patel has said.
The change, which means that an attack on UK soil is now deemed “highly likely”, comes a day after an attack in the Austrian capital, Vienna, that left at least three people dead.
Patel tweeted: “The Joint Terrorism Analysis Centre has changed the UK terror threat level from substantial to severe.
“This is a precautionary measure and is not based on any specific threat.
“The public should continue to remain vigilant and report any suspicious activity to the police.”
Gunmen – believed by Austrian police to have an Islamist motive – killed three and left several wounded in Vienna on Monday night as they went on a shooting spree armed with an assault rifle, carrying other handguns, and wearing a fake explosive belt.
First Minister Nicola Sturgeon sent her condolences to Austrian President Alexander Van Der Bellen and Chancellor Sebastian Kurz following the attack.
France is also under alert for Islamic extremist acts amid tensions over a number of recent attacks in the country with links to caricatures of the Prophet Mohammed.
A suspect was arrested last week in connection with a knife attack at the Notre Dame church in Nice in which three people were killed.
That incident came just weeks after an attacker decapitated a French middle school teacher who showed caricatures of the Prophet Mohammed for a class on free speech.
Assistant Commissioner Neil Basu, UK head of Counter Terrorism Policing, said the public should remain alert but not be alarmed by the change in threat level.
He said: “Since 2014, when the threat level was last changed from substantial to severe, we have continued to build on our capability and enhance security arrangements against the backdrop of a consistently high level of threat. Officers work day and night to protect the public and keep them safe from the threat of terrorism and this will not change.
“We have activated the established planning mechanisms across the police service, which will lead to enhanced protection and preparedness.
“Some of this will be visible and involve additional police officers being deployed to certain places and locations, which the public can expect to see over the coming days.”
Police Scotland Assistant Chief Constable Angela McLaren also urged people to remain vigilant and report any suspicious activity.
The five terror threat levels in the UK are:
Low – an attack is highly unlikely
Moderate – an attack is possible, but not likely
Substantial – an attack is likely
Severe – an attack is highly likely
Critical – an attack is highly likely in the near future