Police are trying to establish a motive for separate pipe bomb attacks in County Antrim.
The flats were cordoned off after the attack in Rathcoole
The first devices damaged the front doors of two flats in Rathcoole Drive in Newtownabbey just after 2200 BST. It is thought both were empty at the time.
However, residents said many people were in the building and someone could have been injured.
In a second attack in Antrim, two men escaped injury after a device exploded at a ground floor flat.
The attack happened at Carnbrook Drive in the Stiles estate at about 0200 BST. Damage was caused to a bedroom.
The police have appealed for information.