DUBLIN – A 25-year-old Catholic police officer who had just joined Northern Ireland’s police force was killed Saturday when a booby-trap bomb exploded as he got into his car, police and neighbors said.

No group claimed responsibility. But police and politicians universally blamed Irish Republican Army dissidents who have repeatedly planted bombs underneath the private cars of off-duty police officers, particularly new Catholic recruits, in a bid to stop cross-community support for law and order.

Until Saturday, such booby-trap attacks had badly maimed two other officers but killed nobody. It was the first lethal attack on Northern Ireland security forces in more than two years.

The IRA dissidents have stressed their determination to target any Irish Catholics who join the Northern Ireland police force. Building Catholic support for the once Protestant-dominated police force is a central goal of Northern Ireland’s peace process.

“Those who carried out this wicked and cowardly crime will never succeed in dragging Northern Ireland back to a dark and bloody past,” British Prime Minister David Cameron said in London.

And reflecting the exceptional political solidarity in Northern Ireland today, leaders from both the British Protestant and Irish Catholic sides of the community condemned the bombers and vowed to bring them to justice.

“While those behind this act seek to promote division and conflict, let us state clearly: They will fail,” said Sinn Fein deputy leader Martin McGuinness, a former IRA commander who is the senior Catholic in Northern Ireland’s four-year-old unity government.

In Dublin, newly elected Irish Prime Minister Enda Kenny called the killing “a heinous and pointless act of terror.”

And his justice minister, Alan Shatter, vowed that “no effort will be spared in bringing the perpetrators of this dreadful crime to justice.” Many of the IRA dissidents live along the border in the Republic of Ireland.

Neighbors identified the victim in Saturday’s bombing as Ronan Kerr, said he had graduated from the police academy last month, and lived with his mother.