A small device has exploded inside a postal van near the headquarters of MI5 in Northern Ireland.
A fire broke out on Friday morning inside Palace Barracks army base in Holywood, Co Down, the Police Service of Northern Ireland (PSNI) said. The flames spread to two other vehicles and garages within the sprawling complex, which houses Scottish soldiers as well as the secret service.
Dissident republicans opposed to the peace process have attempted to use the postal service several times to target security force installations and government ministers in Northern Ireland and England.
Nobody was hurt in the explosion and fire.
Northern Ireland Secretary Theresa Villiers said: "Those responsible for sending this postal device showed a reckless disregard for the safety of postal workers and others doing their jobs.
"There is nothing to gain from this. Their actions are reckless and futile."
A PSNI statement said on Friday: "Detectives from PSNI Serious Crime Branch can confirm that a small explosion occurred inside the rear of a postal vehicle within Palace Barracks in Holywood this morning."
The postal worker who had been driving the van was not inside when the explosion occurred.
Due to the damage caused by fire and water, the exact nature or make up of the device that caused the explosion has yet to be established, police said.
The Royal Scots Borderers of the Royal Regiment of Scotland have been stationed there since August 2014.
In February 2005, the Government announced that MI5 would take on the lead role for national security intelligence work in Northern Ireland. The threat level from dissident republicans is rated as severe.
Operatives are based at Palace Barracks, close to Belfast and one of the main army bases in Northern Ireland.
The Real IRA has admitted it was behind a car bomb which exploded outside the base in April 2010.
In May this year two bombs were found close to an army reserve base in Londonderry in Northern Ireland's North West.
A series of letter bombs was sent to army recruitment centres in England last year which Scotland Yard linked to dissidents.
Supt Karen Baxter said just after 10:35am on Friday police received a report that a postal van was on fire within the Palace complex.
The Northern Ireland Fire and Rescue Service (NIFRS) attended and extinguished the blaze, however the vehicle was extensively damaged. The flames had also spread to two other vehicles as well as nearby garages, she added.
"Fortunately the postal worker who had been driving this van was not inside when the explosion occurred. Although we have no information to suggest there may be other similar packages in the postal system we are working closely with Royal Mail to mitigate any potential risk."
Democratic Unionist Party (DUP) Stormont Assembly member Alex Easton said: "I am deeply angry and concerned that there has been an attempt to kill somebody or soldiers inside Palace Barracks.
"This is a very worrying development and I would totally and utterly condemn it.
"I am just relieved no one was seriously injured or killed and I would appeal to anyone who has any information to bring it to police to put those involved behind bars where they belong."
Scottish soldiers moved from Dreghorn Barracks in Edinburgh to Palace Barracks in August 2014.