The police officer injured in a dissident republican car bomb attack near Randalstown, County Antrim, is now critically ill in hospital.
Constable Peadar Heffron, 33, is an Irish language specialist for the PSNI and captain of the PSNI GAA team.
He was injured when a bomb exploded under his car on the Milltown Road at about 0630 GMT on Friday.
Mr Heffron has been in the police for 10 years and recently married. He is related to a senior Sinn Fein member.
He had been on his way to work at Woodbourne police station in west Belfast.
It is believed Constable Heffron had driven about a mile from his home when the bomb exploded and he was found breathing and conscious but bleeding heavily.
He underwent surgery at Antrim hospital and was then moved to the Royal Victoria hospital in Belfast.
Chief Constable Matt Baggott said every decent person would condemn the attack.
"Our colleague was brutally targeted this morning in a cowardly attack as he left his home to travel to work," he said.
"Throughout the day I have received messages of support from across the world and all communities.
"My appeal to everyone is that you continue to support us in building peace and to not let this incident detract us all from that goal."
Detective Chief Superintendent Williamson said dissident republicans were responsible for the bombing but it was too early to say which group was behind the attack.
He described it as an "atrocious act of terrorism carried out by cowardly thugs".
"This is an officer who was very prominent in his own community. He is very well-known and very well respected," Detective Chief Superintendent Williamson said.
"The threat is severe, it has been at that level for a number of months now.
"The chief constable and others have emphasised the nature of that threat, that it is severe and that continues to be the case.
"My appeal to everyone in the community, including police officers, would be to be vigilant."
Northern Ireland's first and deputy first ministers issued a joint statement condemning the attack.
First Minister Peter Robinson said is was a "cowardly evil act against a man committed to defending the free society we all enjoy".
"I have said in the past that those who perpetrate such attacks will not succeed in returning Northern Ireland to the dark days of the past. I remain steadfastly committed to upholding that promise," he added.
The deputy first minister, Sinn Fein's Martin McGuinness, said: "These actions serve no purpose and will not further any cause," he said.
The chairman of the Northern Ireland Policing Board, Barry Gilligan, said the bombing was "an attempt to murder".
He added that those who carried it out "cannot be allowed to succeed in bringing any further terror" to the community.
Northern Ireland Security Minister Paul Goggins described it as a "vile attack" which would "sicken people".
SDLP Policing Spokesperson Alex Attwood expressed his "sincere sympathy to the injured young officer" and said that no ground must be conceded to dissidents.
The Alliance leader, David Ford, said he was "appalled at this murderous attack" and added that the bombers were "seeking to drag us backwards into the dark days of the Troubles".
Ulster Unionist South Antrim MLA Danny Kinahan said that while those who carried out the bombing were "intent on undermining the stability of Northern Ireland", the community would reject the "sick acts and beliefs" of terrorists.
Dissident republicans have been responsible for a spate of bomb attacks across Northern Ireland in the last year.
In October, a dissident group planted a bomb under a policeman's car in east Belfast.
His partner suffered minor injuries in the attack.