British Army bomb experts in Belfast have been examining a device that was sent in the post to the Ulster Unionist leader, David Trimble.
The device ignited as a member of staff at the UUP headquarters at Hollywood Road removed it from an envelope.
It is believed there was a single device and no one was injured.
David McNarry, a personal advisor to Mr Trimble, said the device had been intended to cause serious damage.
The device appears to have been in a Jiffy bag and contained matches attached to a video cassette, which ignited when it was opened.
It is not known whether there was any significant quantity of explosives.
It is understood the army has been examining the device in the press room of the UUP's headquarters.
- 1.00 News: Brendan Wright reports on the explosion at UUP HQ in Belfast and the controversy surrounding the outing of the British intelligence agent, 'Stakeknife'.
- 6.01 News: Brian Dobson talks to David Trimble, the Ulster Unionist leader about the incendiary device found at their headquarters today
- News At One: Bryan Dobson talks to David Trimble's personal advisor, David McNarry about the incendiary device found at UUP headquaters earlier

