Two explosions have been reported in Northern Ireland - one near a tourist office, the other near a benefits office in the centre of Londonderry.
Police said no one was injured in the blasts, which happened in Strand Road and Foyle Street.
The Police Service of Northern Ireland evacuated and cordoned off the area following telephone warnings.
Dissident republicans have launched a series of attacks in the city.
Londonderry is preparing to be the UK's City of Culture for 2013 and its organising office for the event has been targeted before.
The explosions happened shortly after 8pm. Residents and businesses in the area were evacuated.
Ulster Unionist leader Tom Elliott said he had no doubt dissidents were behind the attacks.
"These attacks further no cause. They will not create a single job or attract a single pound of investment," he said.
"Londonderry should be enjoying the limelight as the UK City of Culture (next year), yet instead some madmen seem to think it is an opportunity for them to seize some publicity."
He added: "This type of fascism was part of our past. It has no place in our future."