A bomb has exploded in Derry outside the City of Culture offices around 11pm last night.
There are no reports of anyone being injured in the attack, but it is understood the building has been damaged.
It is the second time this year the premises have been targeted - a pipe bomb planted by dissident republicans in January also damaged the offices.
The SDLP MP for the area has said the attackers have shown "complete and utter contempt" for the people of the city.
Mark Durkan said: "Derry's faced a number of challenges and it is winning. The 2013 City of Culture is an opportunity for the city's future."
But he said there are people who are out to destroy and "they don't care if they injure or kill".