Updated

In a landmark verdict, South Korea's top court on Thursday ruled that people can legally reject mandatory military service on conscientious or religious grounds and must not be punished.

The Supreme Court ruling is expected to affect the cases of more than 900 conscientious objectors on trial, as hundreds of South Koreans, mostly Jehovah's Witnesses, are imprisoned every year for refusing to serve in the military.

All able-bodied South Korean men must serve about two years in the military under a conscription system aimed at coping with potential aggression from North Korea. The court broke with its own 2004 verdict that rejecting military service because of religious faith was illegal, saying at the time that confrontation with the North made South Korea's draft an indisputable necessity.

The ruling would be welcome news for those who call for greater individual rights and freedom of opinion in South Korea, though others would criticize it for failing to forget North Korea's threat. When South Korea Constitutional Court ruled in June that the government must introduce alternative social service for conscientious objectors by 2019, a heated debate erupted over whether it's time to come up with such a measure.

On Thursday, the Supreme Court said it quashed a lower court's ruling that sentenced a conscientious objector to 18 months in prison. It says it ordered the lower court to review its earlier verdict. Supreme Court officials said there is little chance the lower court would not abide by the decision.

The majority opinion of a panel of Supreme Court judges is that "conscientious objection of military duty ... can be a valid reason" to avoid military service, the top court said in a statement.

The conscientious objector involved in the case, Oh Seung-hun, welcomed the ruling, saying he'll try to conduct an alternative form of civil service.

"This verdict was possible thanks to the patience of my predecessors and colleagues totaling some 20,000 people," Oh told reporters, according to Yonhap news agency. "I hope there will also be forward-looking and positive rulings in about 930 pending cases too."

South Korea's Defense Ministry has yet to come up with details on alternative service. In 2007 it had considered allowing conscientious objectors to work in special hospitals and take care of people who had disabilities or dementia.