A suspected gun has been discovered close to the scene of a bomb attack near three police officers on a busy coastal path.
A call from a public phone box nearby may also be linked to the explosion on a tow path beside a motorway in north Belfast on Saturday night, metres from officers responding to a report.
Dissident republicans may be responsible but police have yet to attribute the attack, which did not injure anyone. It is the latest in a series of recent attempted attacks on members of the security forces.
Senior investigating officer Detective Chief Inspector Karen Baxter said: "As part of our follow-up inquiries, we now believe that the discovery of a suspected firearm on the tow path could be linked to the attack and I am very keen to speak to anyone who may have been in the area of the tow path before midday on Saturday."
The bomb was discovered when three Police Service of Northern Ireland officers responding to a call around Duncrue tow path near the M5 motorway reported hearing a blast.
Detectives are investigating the possibility that a suspected gun found on the pathway on Saturday morning is linked to the attack. They are also investigating whether a call made from a phone box outside shops at the junction of Antrim Road and Fortwilliam Road in North Belfast at around 7.40pm on Saturday is also connected.
It is too early to attribute the bombing to any group but it is being treated as a terrorist attack, police said.
The finger of suspicion will undoubtedly point to dissident republicans who are engaged in a campaign of violence against security forces in Northern Ireland.
Police received a report of a crime in the area at 1pm on Saturday, and then again at 7pm. When officers attended the scene for a third time, at around 9pm, the bomb exploded.
Ms Baxter has said lines of inquiry include whether the bombers lured the officers to the path and were watching as they approached the device.