Gunmen firing from a passing car killed a Protestant teen-ager and wounded his Catholic friend in north Belfast, where violence has flared for three straight nights. 

The dead 18-year-old, Gavin Brett, had been standing with friends on a sidewalk outside a Catholic sports club in Glengormley, a mostly Protestant suburb, police said Monday. His friend, a Catholic, was hit in the ankle, police said. 

No group claimed responsibility for the attack at 11:30 p.m. Sunday, but police and politicians blamed anti-Catholic outlaws who have been behind much of the recent violence. 

David Ervine, a politician who was once a member of a Protestant paramilitary group, said the gunman was targeting "what was perceived to be a group of Catholics, just returning home from celebrating one of their birthdays. It is ironic, of course, that he turns out to be a Protestant." 

Elsewhere overnight, riot police fended off rival Protestant and Catholic mobs for the third straight night in the most bitterly polarized parts of north Belfast. 

The Royal Ulster Constabulary said its officers were attacked by both sides as they pushed back rioters in three areas where Catholic and Protestant neighborhoods meet. 

For the third night, bursts of automatic gunfire were heard sporadically as militant youths tossed gasoline bombs at police armored cars. No serious injuries were reported. 

Sinn Fein, the Irish Republican Army-linked party that is rooted in the most hard-line Catholic areas, accused outlawed Protestant groups — particularly the Ulster Defense Association — of committing most of the violence in north Belfast in recent weeks. 

During a rally Sunday in honor of IRA dead, Sinn Fein leader Gerry Adams accused the UDA of trying to provoke the IRA into ending its 1997 cease-fire. 

On Saturday night a police officer returned fire after a gunman in a UDA-controlled area fired a burst of bullets at police lines. Nobody was reported wounded. 

Meanwhile, police in the neighboring Irish Republic were interrogating four suspected IRA dissidents after raiding a hotel north of Dublin on Sunday. Under Irish anti-terrorist law the four — who include two men already on bail after being charged with dissident IRA offenses — could be held until Wednesday before being charged or released.