A 52-year-old prison officer has been taken to hospital after a bomb exploded under a van in east Belfast.
The device partially detonated when the man drove over a speed ramp at Hillsborough Drive, off the Woodstock Road, at 07:10 GMT on Friday.
The man's injuries are believed to be serious but not life-threatening.
It is understood the prison officer works in Hydebank Wood Young Offenders' Centre in Belfast.
Northern Ireland Secretary Theresa Villiers told BBC's The Stephen Nolan Show that the attack was "a demonstration of how lethal the terrorist threat continues to be in Northern Ireland".
"Thankfully these incidents happen very rarely but that is only because of the outstanding work of the Police Service of Northern Ireland (PSNI) and their security partners in preventing these attacks from happening most of the time," she added.
Northern Ireland First Minister Arlene Foster and Deputy First Minister Martin McGuinness said it was a "disgraceful and despicable attack".
"Our thoughts and prayers are with this senior prison officer and his family as he is treated for his injuries in hospital," they said.
"We join all right-thinking people in condemning these cowardly actions. As a prison officer, he is someone who serves and protects our community and we are united in our rejection of this attack."
Residents living in the area were left shocked and confused.
A man walking his daughter to school said he heard a really loud bang on Friday morning.
"I thought it was possibly a skip had fallen over, some houses being worked on down the street," he said.
He said the possibility that it could be a bomb "did not enter his mind" and he thought it was related to construction work on the street.
Finlay Spratt from the Prison Officers Association said prison officers had continued to be targeted since the ceasefires and the signing of the Good Friday Agreement in 1998.
"There is no let up for prison officers, we can't live a normal life, we're not allowed to live a normal life by these thugs," he said.
"It doesn't matter how often you condemn it, it just seems to go on and on and they're attacking people who are serving the community, all the community."
A number of residents have been moved from their homes at Hillsborough Drive and an emergency evacuation centre has been opened at the Salvation Army on the Cregagh Road.
The Woodstock Road has been closed at its junctions with Omeath Street and Ravenhill Avenue.
Traffic in the area is being diverted and the road is expected to remain closed for some time.
As a result of the incident, Euston Street Primary School in east Belfast is advising parents that the school can be accessed from Castlereagh Road.
Ulster Unionist leader Mike Nesbitt said he "utterly condemned" the attack.
He said there was "no place for terrorists in my vision of a new Northern Ireland".
Sinn Féin's Gerry Kelly said: "There can be no place for such attacks in our society.
"Those behind attacks like this represent no one and have nothing to offer the community."
Justice Minister David Ford said those responsible for the attack had "shown an utter disregard for human life".
"Those involved in carrying out this misguided attack and those who planned it should see the futility of their actions," he said.
DUP MLA Robin Newton said the person or persons who planted the device "must be condemned by all right thinking people".
"This is a despicable act and it is fortunate that we are not talking about serious injury or even a fatality today," he said.
The police have issued an appeal for anyone who may have witnessed any suspicious activity in the Hillsborough Drive area or surrounding area over the past 24 hours to contact them.