Republican dissidents exploded a bomb near the headquarters of MI5 in Northern Ireland Monday, minutes after police and justice powers were transferred from London.

Hours later, the province voted in its first justice minister to embody those powers, the final piece of a devolution process that began with the Good Friday agreement between pro-Irish Republicans and pro-British Unionists in 1998.

MI5 will continue to play a role in Northern Ireland. The attack, carried out with a hijacked taxi at 24 minutes after midnight, was close to its base in County Down.

"The taxi driver got out (of the car) and shouted 'It's a bomb, it's a bomb!' and we were evacuating the area when it exploded," a police spokeswoman said. An elderly man was slightly injured.

In a call to local media, the Real IRA, which last year killed two British soldiers in the deadliest act of violence in Northern Ireland in more than a decade, claimed responsibility.

Northern Ireland's Deputy First Minister Martin McGuinness of Sinn Fein, which supports the Republican goal of a united Ireland but has renounced violence, said the peace process was "rock solid" and the dissidents' action "futile."

"They are going to fail, and fail miserably, because we have taken up our responsibility as political leaders to build a better future for all of the people we represent," he said.

The Democratic Unionist Party (DUP), which shares power with Sinn Fein in a sometimes fragile alliance, also condemned the attack.

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"As I have said before, the transfer of powers will not be derailed by those who would return us to the darkest days of our past," the DUP's First Minister Peter Robinson said.

"We are as determined as ever to work together to deliver a peaceful and stable society. Today represents another significant step on that journey."

Both Sinn Fein and the DUP had agreed not to put forward candidates for the post of justice minister, which, as widely expected, went to David Ford, leader of the non-sectarian Alliance Party.

Analysts have repeatedly said republican dissidents are likely to remain active and police have said the risk of attack, chiefly on security forces, is severe.

"This is one of the most significant attacks. It's highly political as well as military," said Jon Tonge, a politics professor at Liverpool University.

"They (the dissidents) are showing nothing has changed because MI5 continues to hold the strings. They would regard last night as a major success."

Belfast writer and historian Brian Feeney also said dissidents would remain active in the near-to-medium term, but that "99.9 percent of the population" backed the peace process.

The Good Friday Agreement largely ended three decades of violence that killed 3,600 people from both the Catholic Republican community and the primarily Protestant Unionists.

Dissident Republicans have stepped up attacks recently as politicians hammered out a tortuous agreement on policing and justice that completed the devolution process.

(Additional reporting by Caroline Copley in London and Padraic Halpin and Barbara Lewis in Dublin; Editing by Kevin Liffey)