POSTAL bosses are on high alert over possible further letter bombs sent through the mail to senior PSNI chiefs.
Mail sorting staff have been told to extra vigilant over parcels addressed to top cops and other VIPs deemed under threat from dissident republicans.
On Friday, a second letter bomb addressed to a serving senior police officer was discovered at a Royal Mail depot in Lisburn, County Antrim.
It comes hours after a device in a package addressed to the PSNI chief constable was intercepted at a sorting office in north Belfast.
Assistant Chief Constable Will Kerr said it was thought that dissident republicans were behind both incidents.
He also blamed dissidents for pipe bomb attacks on police vehicles in Derry and the outskirts of Belfast over the last few days.
“All four, along with other attacks this months, have been designed to kill police officers,” he told a press conference.
“We very lucky we are not dealing with a fatality.”
An Army bomb team dealt with the device at Mallusk, north Belfast, early on Friday.
It had been addressed to Matt Baggott at police headquarters in Knock, east Belfast.
Later, a delivery office at Linenhall Street, Lisburn, was evacuated following the discovery of a suspicious object.
The police said that both packages contained a viable device.
Justice Minister David Ford said: “Those who sent these device have no concern whatsoever for sorting office staff who have to be commended.”
Secretary of State Theresa Villiers said the Mallusk attack was “callous and reckless”.
“Those responsible for this device have almost no support and have demonstrated a blatant disregard for the safety of those who could have been injured,” she said.
“The chief constable undertakes a challenging role in delivering community policing in a difficult environment.”
A spokeswoman for Royal Mail said: “The Northern Ireland mail centre at Mallusk was evacuated overnight due to a suspect package.
“Unfortunately there will be an effect on deliveries today and we apologise for any inconvenience this may cause.”
Police have appealed for the public to be vigilant and report anything that looks suspicious.