The attempted murder of an off-duty police officer in Northern Ireland is now being treated as a "terrorist-related" incident, the PSNI has said.
Detective Chief Inspector John Caldwell was shot and seriously injured in front of his young son and others on Wednesday night, after a coaching session at a sports complex in Co Tyrone.
According to police, the attack happened while the detective was loading footballs into the boot of his car when the two men opened fire.
Three men - aged 38, 45 and 47 - were arrested in Omagh and Coalisland on Thursday; a fourth arrest was made, of a 22-year-old, in the early hours of Friday.
Assistant Chief Constable Mark McEwan said: "Following the attempted murder of Detective Chief Inspector John Caldwell on Wednesday... I can confirm that we are now treating it as terrorist-related and our primary line of enquiry is the New IRA".
PSNI Chief Constable Simon Byrne has said that Detective Caldwell remained "critically ill and heavily sedated" in hospital following the attempt made on his life.
Detectives want anyone who was in the area or who witnessed what happened to contact them.
'We stand united'
Sinn Fein's Michelle O'Neill was among political leaders on both sides of the Irish Sea who have condemned the shooting.
Speaking at a news conference on Friday, the First Minister (Designate) of Northern Ireland said "we stand united as one voice in condemnation" of the attack.
"It is so important in moments like this that we stand united.
"And we do stand here united as one voice in our condemnation against this horrific attack on a police officer, someone who is part of our community."
She added: "I think the most powerful message we can send is to stand with the chief constable today and to stand with the police service and to say 'this is not good enough'.
"This is an attack on all of us, this is an attack on our community".
Ms O'Neill was speaking while standing alongside the head of the PSNI and political representatives from the five main Stormont parties - including DUP leader, Jeffrey Donaldson.
Mr Donaldson branded those who carried out the attack as "evil".
"I would say to the evil people who carried out this heinous attack and their organisation: You are not the future of this place. We stand against you," he said.