Petrol bombs have been thrown at an Alliance Party office on the Newtownards Road in east Belfast.
The attack happened at around 11pm on Tuesday and caused scorch damage to the building. No-one was injured.
Two men were spotted running away from the scene.
The office, in which East Belfast Alliance MP Naomi Long is based, has been attacked a number of times since a vote on the flying of the union flag at Belfast City Hall in December 2012.
Ms Long said: "If there are people out there who still believe that fire bombs or other attacks will drive me out, they are wrong.
"Thanks to the PSNI and NI Fire Service for their quick response. Thankfully, damage to office mainly superficial though intent is clear."
First Minister Peter Robinson said: "I condemn without reservation the senseless attack on the East Belfast Alliance Party office. No cause ever advanced by such criminality."
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