SEOUL, South Korea (AFP) — One of South Korea’s largest megachurches said Friday its YouTube worship service was briefly hacked during a live broadcast to display the North Korean flag, with a government agency saying it was checking the details.

The incident occurred early Wednesday morning, when the livestream of the service by the Onnuri Church was abruptly filled with the North Korean flag, accompanied by what appeared to be Pyongyang’s propaganda music.

The flag was displayed for about 20 seconds, a church official told Agence France-Presse (AFP), adding that the incident had been reported to the police.

“During the early morning worship service on June 18, an unexpected video was broadcast due to a hacking incident,” the church said in a separate statement.

“We are currently conducting an urgent investigation into the cause of the incident and will take appropriate measures as soon as the situation is clarified.”

South Korea’s state-run Korea Internet & Security Agency told AFP it was “looking into the case.”

Another Protestant church in Seoul, the Naesoo-Dong Church, told AFP it also experienced a similar hacking incident shortly before its YouTube worship service early Wednesday morning.

An “inappropriate” video was displayed for about 50 seconds due to an “external hacking” attack, Pastor Oh Shin-young told AFP, adding that the footage had no apparent connection to North Korea.

South Korea, widely recognized as among the most wired countries in the world, has long been a target of cyber hacking by North Korea, which has been blamed for several major attacks in the past.

Police announced last year that North Korean hackers were behind the theft of sensitive data from a South Korean court computer network —including individuals’ financial records — over a two-year period.