A pipe bomb exploded today outside a house, police said.
The front door at Ardgrange, Springtown Road, Derry, was damaged but the family inside escaped injury.
Army technical officers attended shortly after midnight and residents in three houses were evacuated.
Detectives appealed for anybody with information to contact them.
Meanwhile, police were also investigating a blast at commercial premises in Tandragee, Co Armagh.
A pipe bomb device exploded at the building in Mullahead Road at around 11.30pm last night.
Damage was caused to the front of the premises.
The building was empty at the time and there were no reports of injuries.
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