Northern Ireland's police watchdog says intelligence officers colluded with Protestant militants before and after their 1994 machine-gun massacre of Catholics watching the World Cup in a pub.

Thursday's report by police ombudsman Michael Maguire caps a five-year investigation into police mishandling of informers within the ranks of the outlawed Ulster Volunteer Force, a pro-British paramilitary group.

Two UVF gunmen attacked a village pub in Loughinisland on June 18, 1994, as Irish Catholic fans watched Ireland's opening World Cup match. Six men aged 34 to 87 died. Nobody was ever charged in the killings.

Maguire says his investigators concluded that police had no warning of the attack, but had permitted informants to smuggle the guns used into Northern Ireland and shielded at least one informant involved in the attack from prosecution.