Police in Northern Ireland have intercepted two letter bombs - one addressed to the Chief Constable and the other to a serving senior officer.
Dissident republicans are believed to have been responsible.
British army bomb disposal teams were called to Royal Mail sorting offices in Mallusk and Lisburn in Co Antrim after postal workers raised the alarm.
The device contained in a package addressed to Matt Baggott at the Police Service of Northern Ireland (PSNI) headquarters in Knock, on the outskirts of east Belfast, was made safe overnight.
The second bomb, sent to a high-profile officer whose identity has not been disclosed, was defused this morning. The discoveries follow two other attempted bomb attacks on police patrols in Derry and Newtownabbey this week.
Assistant Chief Constable Will Kerr said: “It is a definite line of inquiry at this stage that it is a dissident republican grouping of some sort.”
Mr Kerr said it was fortunate no-one was killed or seriously injured. He insisted that morale was high among the rank-and-file officers and said they would not be deterred from doing their duty. “We will continue to deliver a policing service to the people of Northern Ireland irrespective of this threat,” he said. “We have been very successful and we will continue to be successful in disrupting the activities of these small groups.”
Both sorting offices had to evacuated during the alerts, which each lasted several hours. Royal Mail said there would be a knock-on effect with disruption of services throughout the day.
Mr Kerr said there had been a spike in attacks and attempts to kill police officers over the past month but declined to speculate on the reasons for the rise.
“These groups remain dangerous. They may be small, they lack any political objective, they certainly don’t have any support within their own community but they remain dangerous - not just to police officers but to the community at large.”
He said Mr Baggott remained committed to tackling terrorism and delivering day-to-day policing despite the threat to his life. “The Chief Constable is as resolute as his police service to make sure we are not in any way deterred.”
There has been widespread condemnation of the attacks.
Northern Ireland Justice Minister David Ford branded those responsible “senseless”.
Secretary of State Theresa Villiers said the PSNI had her full support.
“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 by this callous and reckless attack,” she said in a statement.
In Belfast, residents have returned to their homes following a security alert at Carlisle Parade in the north of the city this morning.
The bomb squad examined the device at the scene and determined it to be a viable device. The alert ended over shortly before 7.30am. Police are investigating the incident.
PA