A police vehicle is believed to have rammed a car containing the suspects
Three of the five men arrested after an attack on a police officer in County Fermanagh at the weekend have been released without charge.
One of the men had been arrested by Irish police in County Leitrim while two of four men arrested by police in Northern Ireland were also released.
Two other men - aged 41 and 26 - are still being questioned.
It has emerged that members of Army special forces were involved in preventing the attack.
One shot was fired at undercover police in the village of Garrison on Saturday.
Police fired two shots in return but nobody was hurt.
It is understood soldiers from the elite Special Reconnaissance Regiment had monitored the movements of those involved in the Fermanagh attack for a number of days.
It is believed dissident republicans were targeting a Catholic man who joined the PSNI a few weeks ago and travelled back to the village at weekends to visit his girlfriend.
PSNI Chief Constable Matt Baggott has refused to be drawn on whether the military assisted undercover police in foiling the attack.
However, the BBC understands that the Special Reconnaisance Regiment provided the initial information that the officer was being targeted.
Undercover soldiers were then involved in tracking and watching those allegedly involved in the murder attempt for a number of days.
In March the BBC revealed that members of the regiment had been brought into Northern Ireland at the request of the PSNI to help combat the growing dissident threat.
They have been particularly active in County Fermanagh because it was considered to be an area where the threat to police officers was highest.
The detonator went off in a car but the bomb failed to explode in Belfast
Dissidents are also believed to be responsible for leaving a 400lb bomb at the Policing Board headquarters in Belfast on Saturday.
Police say the two attacks were not co-ordinated but the result of coincidence rather than planning.
Politicians have called for tighter security measures to protect Policing Board members and staff after the attempted bomb attack in Belfast on Saturday.
Two men crashed a car through the security barrier at the Clarendon Dock complex at 1900 GMT and abandoned the bomb in front of the board headquarters.
It is thought that only the detonator went off and no-one was hurt.
No one has been arrested in relation to that attack.
Earlier this month, the Independent Monitoring Commission (IMC) reported that the dissident republican threat in Northern Ireland was at its highest level for almost six years.
The IMC said the two main dissident republican groups, the Real IRA and the Continuity IRA, were working more closely together to increase the threat posed to security forces.
Last week, police in Armagh found a mortar bomb which, they said, was intended to kill police officers.