The loyalist Red Hand Defenders have admitted planting a bomb at the offices of Republican Sinn Féin in west Belfast yesterday.
The Red Hand Defenders is a cover name used by the Ulster Defence Association and the Loyalist Volunteer Force.
Republican Sinn Féin is the political wing of the Continuity IRA.
British army bomb disposal experts defused the device - a lunchbox containing an explosive substance with an alarm clock attached to it - in the Beechmount area.
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There were no injuries.
Last week, a letter device addressed to Mr David Trimble went off in the Ulster Unionist Party's headquarters in east Belfast.
A Continuity IRA bomb was also defused last month outside the offices of Democratic Unionist MP Mr Nigel Dodds.