Nine people – including a child – escaped injury after pipe bombs exploded at their homes in racist attacks.
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.
Around the same time another pipe bomb exploded outside a house in the Lincoln Court area of the city.
The front door was damaged but the four adults inside the property were not injured.
SDLP Assembly member for Foyle Pat Ramsey said two Romanian families had been targeted.
"It appears that this appalling attack on homes in Derry was racially motivated; this is a very disturbing development," he said.
"The devices used were viable and this disgraceful attack must be condemned by all in our community.
"My thoughts are with the families who have been targeted and endured such a terrifying experience during this unacceptable attack.
"We must value, respect and accept our migrant community living in the city.
"Migrant workers are making a significant contribution to our economy and our society.
"Those responsible must face the full rigour of the law."
DUP councillor Drew Thompson said a letterbox had been blown off the door of one of the houses.
"One family said to me they heard a bang at about half past one and they ran out, not thinking," he said.
"They couldn't see anything, but it was only later on that they realised that there had been a partial explosion."
Remains of the devices were taken away for forensic examination. Police urged anybody with information to come forward.