Two explosions in Londonderry forced elderly residents to leave their sheltered accommodation.
Homes and businesses in the city centre were also evacuated after police received two telephone bomb warnings shortly after 7.30pm yesterday.
Nobody was injured by the blasts shortly after 8pm close to a tourist office and DHSS premises in a busy centre for nightlife and shopping. Dissident republicans were blamed by politicians.
Police Service of Northern Ireland district commander in the city, Chief Supt Stephen Martin, said his men had acted swiftly.
"The reckless acts of those who planted these devices stand in stark contrast to those of the brave officers who entered these areas to evacuate local residents and businesses," he said.
"The people in Derry do not want this disruption. It is cowardly and callous."
Next year Londonderry is the UK City of Culture. Dissidents have targeted the organising committee's offices before as well as a police station on Strand Road. Last night's attacks happened in Foyle Street and Strand Road.
Mr Martin added: "People simply want to move on with their lives, not take a step back. Regrettably the whole community will once again suffer as a result of the needless actions of a few.
"We will experience major traffic disruption and life will be severely disrupted in the city."
The area has been cordoned off and forensic examination will go on for much of today.
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.
"This type of fascism was part of our past. It has no place in our future."
Justice Minister David Ford said: "These are the desperate actions of yesterday's men. They seem to be more wedded to the struggle than to the cause they claim to be pursuing."