A dissident Republican group calling itself the "New IRA" has said it carried out the attack on a prison officer in Belfast on Friday.
The claim was made in a statement to the BBC.
The 52-year-old prison officer was seriously injured wheh a bomb exploded under his van on his way to work.
Three men and a woman were arrested yesterday in connection with the attack.
The explosion occurred in the Hillsborough Drive area off the Woodstock Road in the east of the city.
The prison officer is based at Hydebank Wood Young Offenders Centre in south Belfast and works as a trainer for new recruits to the NI Prison Service.
Following the attack, police commanders expressed fears it may be the first of a number of dissident republican murder bids launched to mark the centenary of the Easter Rising.
