Police in Northern Ireland are asking the public to remain vigilant after a viable letter bomb was addressed to the PSNI's Chief Constable. 

The device was discovered at a Royal Mail sorting office on the outskirts of north Belfast in the early hours of this morning. 

An army bomb disposal unit worked through the night and successfully diffused the device. 

The package was addressed to Chief Constable Matt Baggott at Police Headquarters in Knock on the edge of east Belfast.

PSNI officers are asking anyone who noticed suspicious activity in the area to contact them.