Two men were shot dead and four more were injured Saturday night when gunmen opened fire outside a military barracks, police said.
No one immediately claimed responsibility for the attack at Massereene Barracks northwest of Belfast, but suspicion is likely to center on dissident republican groups opposed to the Irish Republican Army's cease-fire.
The victims were not immediately identified.
"There have been two fatalities. It is understood that those two fatalities are male," said a police spokesman, speaking on condition of anonymity in line with department policy.
"It is also understood that a further four males have been brought to hospital and are in a serious condition."
Witnesses reported hearing two long bursts of gunfire.