The headquarters of Mr David Trimble's Ulster Unionists were targeted in an overnight paint bomb attack.
At least seven bags of paint were thrown at Cunningham House on the Holywood Road in East Belfast during the early hours of this morning.
Earlier this week Mr Trimble's constituency office in Lurgan was targeted in a similar attack.
The paint bombing occurred during the final weekend of Northern Ireland's Assembly Election campaign.
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The Ulster Unionists are involved in a fierce battle with the Rev Ian Paisley's Democratic Unionists to hold on to their position as the leading unionist party in next Wednesday's Assembly elections.