A Protestant paramilitary organization claimed responsibility Friday for killing three young Catholics at a mobile food shop, declaring it a reprisal for an Irish Republican Army attack and warning of further killings.

The Protestant Action Force, the cover name for the outlawed Ulster Volunteer Force, said it carried out the murders Thursday night of two teenage girls inside the shop and a 29-year-old man who rushed to their aid because the business owner was a "known IRA killer" and one victim was a supporter.