SEOUL (THE KOREA HERALD/ASIA NEWS NETWORK) - A 23-year-old South Korean man is under investigation for allegedly seeking to join the Islamic State in Iraq and Syria (ISIS) terrorist group, and preparing for a terrorist attack while he was serving in the army.

It marks South Korea's first case of a "lone wolf" terrorist act being planned.

The man surnamed Park, 23, was found to have stolen an ignition device for explosives while being trained at an army engineer school after joining an infantry unit near Seoul in October 2017, broadcaster KBS reported.

He allegedly propagated and instigated ISIS terrorist activities by collecting videos and materials of the group's acts and uploading them on the Internet from 2016 until recently.

A video showing how to make live ammunition was found on Park's mobile phone, and a machete, or a broad blade that looks similar to the weapon often used by terrorists, which he bought online was found at his home.

A joint team of investigators from the military and police also reportedly found that Park installed a secret app used by ISIS members and supporters on his mobile phone, and received an e-mail from a person believed to be an ISIS member on how to join the terrorist group.

Police began the investigation upon receiving intelligence from the US Federal Bureau of Investigation last year, and informed the military after confirming that Park was on active duty.

The Ministry of Defence said that the investigators sent Park to the ministry's prosecutors office on July 1 for indictment on charges of stealing military equipment and violating the counter-terrorism law.

As Park was discharged from military service on July 2, however, military prosecutors will look into his alleged theft of military equipment, while civilian prosecutors investigate his alleged counter-terrorism law violations.

If convicted, Park will be the first South Korean to be punished in the country for planning terrorist acts in liaison with an international terrorist organisation since the counter-terrorism law went into effect in March 2016.

The ISIS claimed responsibility for a series of suicide attacks against churches and hotels in Sri Lanka in April that killed more than 320 people, just a month after the US said it has defeated the international terrorist group.