Two police officers were injured when an explosive device was thrown at them at a toy shop in Newtownabbey.
They suffered facial wounds, which are not life-threatening, in the blast when they were summoned by an alarm to the Toys R Us store in Mill Road shortly after midnight. Two staff members also suffered shock.
Dissident republicans have used the method of setting off alarms to lure in PSNI officers before, including in north Belfast.
Police condemned those responsible.
“This was a despicable act, not only on police officers responding to a call for assistance but also on two members of the public," said Chief Inspector Derek McCamley.
“We are extremely fortunate that no-one was more seriously hurt.”
He promised a full investigation but said it was too early to say who was behind the attack.
“I have spoken with my officers this morning and was struck by their steadfast determination to continue providing the personal, professional, protective service the community want and deserve,” he added. “Those behind this attack are cowardly individuals who only seek to bring devastation and harm to their own community.
“We will not be deterred from our job of keeping the community safe.”
People living close to the scene of the attack had reported hearing a loud bang, but said they thought it was fireworks.