The Police Service of Northern Ireland said one of its officers has been shot to death in an ambush in Craigavon, a town southwest of Belfast.
Monday's attack in Craigavon's Lismore Road area, a predominantly Irish Catholic area, came two days after Real IRA dissidents shot and killed two British soldiers at an army base in the town of Antrim. Two other soldiers and two pizza delivery men were wounded in that attack.
No group is claiming responsibility for the latest shooting.
Dissidents opposed to Northern Ireland's peace process and the Catholic-Protestant government it forged have been increasing their attacks against British security forces in recent months.