Image copyright Pacemaker Image caption Three fire appliances were sent to deal with the fire at a vehicle in Palace Barracks

An explosion at an army base in Northern Ireland may have been caused by a firebomb, the BBC has been told.

Police have confirmed that a device exploded inside a Royal Mail post van at Palace Barracks in Holywood, County Down, before 10:30 BST on Friday.

The subsequent blaze spread from the vehicle to two cars and three garages. There are no reports of any injuries.

The postal worker who had been driving the van was not inside when the explosion happened.

Image copyright Pacemaker Image caption The blaze spread from the postal van to two cars and three garages nearby

Firefighters attended the scene for about 90 minutes and police forensic experts spent several hours examining the burnt-out remains of the van.

Supt Karen Baxter said: "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.

"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."

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Theresa Villiers, the Northern Ireland secretary of state, 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."

Image copyright Pacemaker Image caption Soldiers from the Royal Scots Borderers have been stationed at the barracks since last August

In April 2010, a bomb planted by the Real IRA, a dissident republican group, exploded outside the army base which houses MI5's Northern Ireland headquarters.

The explosion happened minutes after policing and justice powers were devolved to Stormont from Westminster.

During the three decades of the Troubles in Northern Ireland, Palace Barracks served as a base for British army battalions.

Soldiers from the Royal Scots Borderers, 1st Battalion the Royal Regiment of Scotland have been stationed at the barracks since August last year.