Dissident republicans tried to murder police officers during an attack in Craigavon, County Armagh, the Police Service of Northern Ireland (PSNI) has said.
At about midnight on Friday, a loud bang was heard in the Tullygally Road area of the town.
A “viable device” was later found.
Police said it is unclear if the device was fired at a passing patrol or if the attack was set up to target officers responding to calls from the public.
PSNI Ch Insp Barney O’Connor said he could not condemn strongly enough those behind the “cowardly and despicable act of terrorism”.
He said their actions offered nothing to the community.
“At this stage we believe the device to be viable and that this was an attempt by dissident republican terrorists to murder police officers,” he added.
Homes have been evacuated in the area and diversions are in place.
Police said that a short time after the bang, they were contacted by a Belfast-based newspaper which reported that a call had been made to it claiming a device had been fired at a police patrol, but had missed its target.
“We responded along with ATO colleagues and a suspicious object was located,” Insp O’Connor said.
Once the security operation is over, police said the device will be removed and forensically examined.
Sinn Féin MLA John O’Dowd said those behind the attack have “no support”.
“So, who are they serving other than themselves? Who were they serving last night when they tried to kill police officers?
“If there’s anybody in those organisations that is prepared to listen, I would ask them to stop immediately.”
In 2009, PSNI Constable Stephen Carroll was shot dead by dissident republicans as he responded to a 999 call in Craigavon.
He was the first police officer to be killed since the formation of the PSNI in 2001.