Police are investigating the motives for two separate arson attacks in Londonderry and Armagh.
A house in Henry Street in Derry was damaged when a petrol bomb was left outside the front entrance at about 0300 GMT on Saturday.
The police are investigating if the attack was sectarian.
Meanwhile, a fire was started inside a house in Mullacreevie Park, Armagh, at about 0445 GMT after a rear window was smashed.
A sitting room in the house was damaged.
Police have said that no one was in either house when they were attacked and have appealed for information.