The PSNI is investigating an incident in Lurgan, Co Armagh, which may have been an attempt to kill some of its officers.
A Sinn Féin Assembly member living in the area, Northern Ireland Education Minister John O'Dowd, believes dissident republicans were responsible for exploding a device in a bin while police were in the area.
Police had travelled to the North Circular Road and Levin Road district following reports that an illegal parade was being planned.
In March 2009, PSNI Constable Stephen Carroll was shot dead in nearby Craigavon, while he was responding to what was a bogus 999 call.
Separately, a pipe bomb exploded in the Ardaveen area of Bessbrook, Co Armagh, just before midnight.
There were no reports of any injuries.