Two explosions hit separate locations in Derry City at 8pm this evening.
The first explosion occurred close to the tourist office in Foyle Street. The second blast happened on Strand Road near the social services office.
Nobody was injured in the explosions.
The PSNI believes dissidents are responsible for the attacks.
It said that coded telephone warnings were received before both attacks at 7.30pm.
Homes and businesses were evacuated and the area was cordoned off following the warnings.
A number of elderly residents from sheltered accommodation in the Bridge St area were also forced to leave their building.
The PSNI in Strand Road is asking for anyone with information to call 0845-6008000, or the Independent Crime Stoppers charity anonymously on 0800-555111.
