The blaze at Arvalee School and Resource Centre began shortly before midnight on Friday.

Investigating officers want to speak to a number of people seen in and around the area of the fire.

They are appealing for two males - one of whom had long dark hair and a beard - seen pushing a wheelbarrow in the Hospital Road area to come forward.

Several fire appliances attended the scene and firefighters worked throughout the night to contain the blaze, a spokesperson for the Western Education and Library Board (WELB) said.

"The cause of the fire is currently under investigation and the level of damage sustained in terms of both building and resources will be assessed over the coming days.

"Board staff are working closely with the Principal of Arvalee School and Resource Centre, Jonathan Gray, and are making every effort to ensure that suitable temporary accommodation is sourced for pupils and staff as soon as possible," the spokesperson added.

Staff are due to meet with the principal on Monday followed by a meeting with pupils' parents on Tuesday.

Education Minister John O'Dowd visited the scene and said the fire will have "a devastating impact on the whole school community."

The school caters for some of the most vulnerable children in our society and this fire will cause great distress just as the pupils are preparing to return for a new academic year.

John O'Dowd

The Sinn Féin minister continued: "The impact will go further; this also affects the parents, staff and the wider community in Omagh."

Mr O'Dowd said he was disturbed to learn the fire is currently being treated as suspicious.

"Whilst I struggle to comprehend who might wish to do this to a special school, I would ask that if anyone has information on the blaze, they take it to the PSNI."

He said alternative arrangements would be made as quickly as possible to ensure that "any distress to the children involved is kept to an absolute minimum."

"I had already announced a new build for Arvalee School and Resource Centre as an early development on the Lisanelly site. I will want to explore with my officials and other stakeholders how we can advance the timetable for that given last night's events.

West Tyrone MLA Tom Buchanan has spoken of the shock and sadness in the area over the fire.

"Arvalee school is a facility used by all sections of the community and there is a real sense of shock and sadness that anyone might have set out to deliberately attack it," the DUP politician said.

"My colleague Cllr Errol Thompson, who is Chairman of Omagh District Council, was on the scene during the night and has spoken to many local residents. The sense of shock goes right across the Omagh District as Arvalee is not just a school but truly is a community facility."

Mr Buchanan has urged anyone with information, or who may have witnessed suspicious activity in the area, to contact the PSNI.

"My thoughts are with the staff and with the many pupils who will be greatly distressed that their school appears to have been attacked in such a way. One of the immediate priorities now is obviously to ensure that temporary accommodation can be provided as it is vital that the work of the school continues."