STAFF at post sorting offices have been warned to be on high alert after a letter bomb was sent to police headquarters in Belfast.
Sources revealed that the device was posted from the Republic and addressed to Chief Constable of the Police Service of Northern Ireland (PSNI) George Hamilton.
The alert was raised yesterday after a suspicious package in a brown padded bag with a white address label was received through the post.
An army bomb disposal team was called to the scene where they made the device safe.
Management at sorting offices urged staff to be on high awareness following the discovery, the Irish Independent has learned.
A spokesman from An Post said it "will be guided by the advice we get from the gardai".
"We work very closely with the gardai in these situations and that will be what will happen here," the spokesman added.
The shock discovery comes six months after a viable device was found at a post sorting office in the North.
The alarm was raised when a letter bomb was recovered at Northern Ireland's main post sorting office last July.
The device was recovered at an office in an industrial estate in Newtownabbey, near Belfast.
It marked the re-emergence of a terror tactic formerly used by paramilitaries during the Troubles.
PSNI Superintendent Sam Donaldson described the latest discovery as "a mindless and foolish act".
The Knock Road was closed between Kings Road and Cherryvalley during the investigation.
Mr Donaldson said: "This is a mindless and foolish act that could have resulted in the serious injury of any person handling the package.
"Although we have no information to suggest there may be other similar packages in the postal system, I would encourage people to be vigilant."
In 2013, dissident republicans opposed to the peace process were blamed for sending a series of letter bombs to high-profile figures in the North. One was sent to the seat of the Executive at Stormont Castle in Belfast, addressed to Northern Ireland Secretary Theresa Villiers.
Another bomb was delivered to the offices of the Public Prosecution Service in Derry, while two explosive packages, addressed to former PSNI Chief Constable Matt Baggott and one of his senior commanders, were intercepted at Royal Mail offices in Belfast and Lisburn.