Ocean Terminal received a threat. Picture: Scott Louden

The message – which bears similarities to previous online hoaxes – warns of “gun men” and “explosives” at Edinburgh College’s Sighthill and Granton campuses, Napier University, Ocean Terminal and Currie Community High School.

It insists these locations will be under “imminent threat” between today and May 5 – and “strongly” recommends they are evacuated.

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The note found on the back of a toilet door. Picture: Facebook

The author claims to have overheard a conversation in a “secret” bar in Edinburgh or Glasgow warning of the upcoming incidents.

The warning, written on the back of a toilet door at Edinburgh College’s Granton campus, reads: “There is an imminent threat possibly heading towards these locations involving gun men and/or explosives.

“I also suggest the police do a thorough search at all the bars and clubs in Leith, Edinburgh, and check for secret room entrances within the bars themselves.”

It continues: “The individuals behind these plans are absolute lunatics and extremely delusional. They have done some nasty stuff in the past that have led me to believe that this is a legitimate threat.”

The note found on the back of a toilet door. Picture: Facebook

Officers revealed they were investigating the message but insisted inquiries were still at an early stage.

Doreen McKinnon, headteacher at Currie, sent a letter to parents yesterday afternoon to inform them that police were carrying out a “full investigation”.

She said: “I wish to reassure you that we are following police advice and if the police advice is that further action is required we will act without hesitation. The safety of pupils and staff is paramount.”

Napier University and Ocean Terminal declined to comment on the threat, while Edinburgh College could not be contacted at the time of going to press.

A police spokesman said: “Police in Edinburgh are investigating reports of a threatening communication that was found on a bathroom door within an education building in north Edinburgh on Monday, April 18.

“Inquiries are at an early stage and police are working closely with partners to provide reassurance to the public.”

Online hoaxes about imminent bomb attacks are frequently shared on social media. Often, an internet poster will claim they were tipped off about an impending attack after helping a stranger on the street – who turned out to be a terrorist.

In February, bomb threats in Edinburgh forced the evacuation of Tynecastle High and the Royal High, while Boroughmuir High was also searched by police.