Gardaí have finished their technical examination at two houses on the same street in Dundalk after separate fires broke out last night.
The first fire started at around 6 p.m. in the Muirhevnamore estated and the second blaze broke out at around 10 p.m.
It is believed one man was in the first house at the time of the fire. He was taken to hospital suffering from smoke inhalation.
The second house was empty when the blaze started. Gardai are treating both fires as suspicious.
A Garda spokesman said the investigation was continuing. No arrests have been made.