The Taoiseach said today he had no doubt the Real IRA was responsible for planting a car bomb which exploded in the English city of Birmingham last night.
"We have got to deal with this on a security basis", Mr Ahern told RTÉ radio, because the dissidents will not listen to reason.
Mr Ahern extended his sympathy to those affected by the bomb which resulted in no injuries.
The Chief Constable of the new Police Service of Northern Ireland (PSNI) Sir Ronnie Flanagan confirmed dissident republicans were the chief.
Earlier British police also blamed dissident republicans for the car bomb explosion at Smallbrook Queensway, Birmingham, near to New Street railway station, at 10.30 p.m.
There were no injuries and the bomb appeared to have caused minimal damage despite being detonated in the heart of the city, close to theatres, nightclubs, bars and restaurants.
Unconfirmed reports today suggest that the bomb did not fully explode.
The damage to the car which contained the bomb was confined to the boot area and there was no damage to surrounding buildings or other vehicles.
It is believed that only the detonator on the device exploded and that the device contained between 30 and 50 kilos of explosive.
No group has admitted responsibility for the blast although suspicions are likely to fall on republican dissident group the Real IRA. It is understood that the bombers used a recognised codeword, when warning of the impending blast.
The telephoned warning was not made to police and officers declined to comment on who had received it. They say the warning did not give officers sufficient time to evacuate the area.
Mr Flanagan told BBC's Breakfast with Frost programme: "In discussion with my colleagues in Great Britain, even though it is at an early stage, we do believe it is a dissident grouping - probably that group that is behind this.
"They want to demonstrate today that they are still there but I have to say that through all the good work of policing colleagues right throughout the world ... thankfully at this stage - although we cannot be complacent about their intentions - their desire far exceeds their ability.
"It is our job to continue to ensure that is the case."
Last night passers-by described what appeared to be a powdered substance coming from the back of the car, sparking fears of an anthrax attack.
Chief Inspector Ellie Bird, of West Midlands Police, said that two or three police officers were decontaminated as a precaution before it became apparent that the bomb was the work of dissident republican group.
The officer added that anti-terrorist experts from the Metropolitan Police and army bomb disposal specialists were today at the scene, which has been cordoned off.
Ms Bird said: "Early indications are that this is the work of an Irish dissident group. There are no connections with events in America."
Birmingham was the target of the IRA in 1974 when 17 people were killed in a bombing.
Ms Bird said: "We are very relieved that there have been no serious injuries. There were people in the area as this is a very busy part of Birmingham city centre."
She said a 1,000-metre cordon had been placed around the blast site, adding: "Until we are satisfied that it's safe, it will remain sealed off.
"It would appear that the damage has been very minimal with damage to the vehicle itself only.
PA