DUBLIN — The most notorious Protestant militant of Northern Ireland's conflict, Michael Stone, must stay in prison for attacking an Irish Republican Army funeral in 1988, the top judge in the British territory ruled Monday.

Monday's Court of Appeal judgment by Lord Chief Justice Declan Morgan means Stone, 58, cannot be considered for parole until at least 2018, according to the Northern Ireland Prison Service. His lawyers had sought immediate parole from his 30-year sentence.

Court officials initially interpreted Morgan's order to mean that Stone must stay in prison until at least 2024, not 2018, because he had received a six-year parole that ended in 2006, when he tried to attack the Northern Ireland Assembly. But the Prison Service said parole would be considered — though not necessary awarded — 30 years after the date of his funeral attack.

Morgan said Stone posed a special danger to society. He had demonstrated no remorse and was a professional killer responsible for two of the most high-profile attacks in Northern Ireland history.

"There are serious aggravating factors. The effects on victims will live with them forever," the judge said.

Stone became a celebrated figure among Protestant extremists when he launched a solo gun-and-grenade attack on an IRA funeral in March 1988. He threw grenades into a crowd of thousands, wounding about 60 people, and shot to death three men — among them an IRA member — who pursued him on foot. After running out of ammunition, Stone was nearly beaten to death by mourners before police intervened.

Protestants who sought to meet IRA violence tit-for-tat lauded his strike. A 1990s Belfast wall mural depicted him shooting, one gun in each hand, from behind a row of headstones. "We killed 3 with one Stone," it said.

Stone told The Associated Press in a 1992 prison interview that his only regret from that day was his failure to time his grenade throws better, because they exploded in long grass and not in the air, where they probably would have caused worse casualties. Stone said he had hoped to kill Gerry Adams and Martin McGuinness, leaders of the Irish nationalist Sinn Fein party, who were at the IRA graveside but not injured.

He received a 30-year prison term for six murders, including the killing of three Catholic civilians from 1984 to 1987, and five attempted murders. But like more than 500 paramilitary convicts, he received an exceptional parole following Northern Ireland's Good Friday peace accord of 1998.

After his 2000 freedom, Stone tried to reinvent himself as an artist, opening a gallery in Protestant east Belfast and selling his often cartoonish paintings to Belfast politicos.

But his hatred of the compromise at the heart of the Good Friday deal — a power-sharing government that included Sinn Fein — led him on another one-man assault in November 2006. His target this time was the Stormont Parliamentary Building in Belfast as lawmakers faced a deadline to form a new Catholic-Protestant coalition.

He arrived at Stormont armed elaborately with an ax, knives, a garrote designed to strangle a victim, and a gym bag containing explosives, fuel and fuses. But slowed by a debilitating neurological disorder, Stone couldn't push past the front-door security detail and was photographed, humiliatingly, being strong-armed to the ground by two guards.

Stone's defense team contended he never intended to kill but was engaged in "performance art." Their argument was undercut by Stone's own handwritten message to Belfast media hours before his attack saying he hoped to kill Adams and McGuinness the second time around.

He received an additional 16-year sentence for attempted murder of the Sinn Fein chiefs, though this punishment in practice did not add even a day to his resumed incarceration.