A prison officer injured in a dissident republican bomb attack in Northern Ireland earlier this month has died.

Adrian Ismay, 52, was seriously hurt after a booby-trap device exploded under his van in Belfast on 4 March.

It is understood he died from a heart attack after being rushed back to hospital on Tuesday morning.

Chief Constable George Hamilton said police would have to wait for medical evidence before confirming if his death would be treated as murder.

A post-mortem examination is expected to be carried out on Wednesday and Det Ch Insp Richard Campbell, the senior investigating officer in the case, said the results would inform the course of his inquiry.

"I think we need to be careful and see where the evidence takes us in this investigation," he added.

A dissident republican group widely referred to as the new IRA said it carried out the attack .

The organisation said Mr Ismay was targeted for training officers at Maghaberry Prison near Lisburn, County Antrim.

Well-placed prison sources said some dissident republicans in the prison celebrated the news of Mr Ismay's death, taunting prison officers by smoking cigars in the exercise yard of their wing.

Mr Ismay, a father-of-three, was discharged from hospital a week ago and police said his injuries were not as serious as first thought.

On Tuesday, Det Ch Insp Campbell said Mr Ismay's death had come as a "real shock to the investigation team, but much more so to Adrian's family and friends".

The detective appealed for information on two cars that police believe may have been used by the bombers.

"The first one is a red Citroen C3, registration SKZ 6662, which I believe was used by those planting the device at Hillsborough Drive [at about 02:20 GMT on] Friday 4 March," Det Ch Insp Campbell said.

"The second vehicle is a silver Skoda Fabia, KFZ 2352, which I believe was used before and after the incident by those involved."

He said police understood that a man was dropped off from the Skoda in Pilot Street, near Belfast docks, at about 03:00 GMT on the morning of the bombing.

Both cars were seized by officers immediately after the attack.

Police have asked the public for help in tracing the movements of the vehicles before the explosion.

Northern Ireland First Minister Arlene Foster said she was "personally devastated" by Mr Ismay's death.

She tweeted , external : "Can't believe the news. I was texting Adrian before we left for the US. He was doing well. My thoughts are with his family."

Deputy First Minister Martin McGuinness said those who had targeted the officer had no support for their actions.

Justice Minister David Ford and Sue McAllister, the director general of the Northern Ireland Prison Service, paid tribute to Mr Ismay.

"Adrian Ismay gave over 28 years of service to prisons in Northern Ireland and he was greatly respected by all those who knew him," they said in a joint statement.

It was understood the prison officer worked at Hydebank Wood young offenders' centre in Belfast.

A man appeared in court last week charged with attempted murder in connection with the bomb attack.