The Police Service of Northern Ireland has praised the "bravery" of officers who rescued four people from a house fire in Dungannon, Co Tyrone last night.
Two of them - a man and a woman - are in a critical condition, while two children are said to be stable in hospital.
Eight PSNI officers were also taken to hospital after the blaze broke out at Cunninghams Lane in Dungannon at around 8.30pm.
A 21-year-old man and a 15-year-old boy have been arrested on suspicion of arson and are currently being questioned by police.
In a statement, the PSNI said: "A 15-year-old male has been arrested on suspicion of arson with intent to endanger life, and remains in police custody at this time, assisting with enquiries.
"A 21-year-old man also arrested on suspicion of arson with intent to endanger life also remains in police custody this evening.
"Four people were taken to hospital following the fire, which occurred shortly after 8.30pm on Monday evening.
"A man aged 37 and a woman aged 70 remain in a serious condition, while two children, aged 7 and 10, are in a stable condition."
Watch: PSNI officers praised after Tyrone house fire rescue
The "fire was started deliberately", according to Deputy Chief Constable Bobby Singleton, who added that "it's hard to comprehend the mindless cruelty of this act, and the panic and fear caused to those in the home".
In a statement, Mr Singleton said "the house was well alight" when police - the first emergency responders - arrived at the scene.
"Officers obtained two ladders from neighbouring properties and were able to rescue an unresponsive 70-year-old woman and a young child from the rear of the property.
"A number of the officers then entered the house and brought a second child and a 37-year-old man to safety.
"The adults remain in a critical condition in hospital ... while the children, thankfully, as we understand are presenting in a stable condition.
"Eight officers from the Local Policing Team in Dungannon, two Sergeants and six Constables, were taken to hospital after the fire, including one officer who collapsed after rescuing one of the children from the property," Mr Singleton said.
"I am extremely thankful that our colleagues were released in the early hours of this morning following treatment, although they are still suffering the after effects of smoke inhalation and will be absent from work as a result.
"I want to acknowledge the bravery of our police officers, whose only focus when entering the burning building was the safety of those inside.
"They exemplify the qualities we know are held by so many of our colleagues - courage, selflessness and a focus on our community.
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"I also want to thank our colleagues from the Northern Ireland Fire & Rescue Service and Northern Ireland Ambulance Service, alongside the residents of Cunninghams Lane, for their support.
"A police cordon remains in place as we work alongside the Fire Service to establish the cause of the fire, and we thank the local community for their ongoing patience and co-operation.
"I am aware that videos and photographs of the fire and events surrounding it are circulating on social media.
"We would ask that people be mindful of the victims of this despicable attack, and refrain from sharing this footage," Mr Singleton said as he urged people with information to contact the PSNI.
