The lethal devices detonated at the properties lived in by families from Romania.
Police are treating the incidents in the Waterside area of Londonderry in the early hours of Saturday as hate crimes.
They follow a series of racist attacks in Belfast in recent months.
Shortly after 1.35am, officers received reports a pipe bomb had exploded outside a house in the Lapwing Way area.
No damage was caused to the property and four adults and one child who were in the house at the time were not injured.
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