A petrol bomb has been thrown at a house in an early-morning attack in the Belvoir area of south Belfast.
Police were called to the scene of a fire on Downhill Avenue shortly after 1.43am on Sunday.
Officers attended along with the Northern Ireland Fire and Rescue Service to extinguish the blaze.
Detective Sergeant O'Flaherty said: "Significant damage has been caused to the front door of the porch. A man and woman, who were inside the property at the time, were fortunately uninjured.
"We are treating this as arson," the statement added.
"And had the fire not been extinguished so quickly, the consequences could have been devastating.
"I am appealing to anyone with information, or who noticed any suspicious activity in the area, to contact us on 101 quoting reference number 163 of 17/05/20."