A man has been arrested and questioned by police investigating gorse fires in the Mullaghfad area of Fivemiletown in County Tyrone.
The 55-year-old was detained yesterday afternoon and has since been released on police bail.
The blaze spread across a 5 kilometre area, crossing the border.
The Fire Service said it has fought more than 500 gorse blazes since the start of this month - including 466 which were started deliberately.
Police said that almost 250 fires had been reported since May 1.
But the Fire Service has updated the figures and said it had attended 511 gorse fires between May 1 and yesterday afternoon.
It said its stations in Downpatrick, Co Down, and Lurgan, Co Armagh, were busiest, dealing with 46 and 41 fires respectively.
The service said the blazes not only put firefighters' and residents' lives at risk but also put extra pressure on its resources.
Around 60 firefighters spent five hours tackling a deliberate blaze close to St Mary's High School in Newry between Friday night and Saturday morning.
Area Commander Maurice Rafferty appealed to anyone who notices a fire to report it to the service and leave the area as soon as possible.
"Deliberate fire setting has major consequences - it ties up our vital resources from other more serious incidents and potentially puts people and property at risk," he said.
"These fires can easily spread and even a slight change in wind direction can pose a serious risk to life, property and the environment. If anyone has any information in relation to fire setting we would urge them to contact the PSNI.
"I would like to thank our crews who have worked under extremely hazardous conditions and intense heat to bring the fires under control."
