The state-run nuclear energy research center, which is suspected of having been a target of a cyberattack by North Korea, confirmed that there was outside access to its system.

Speaking to KBS on Friday, the Korea Atomic Energy Research Institute(KAERI) said it was notified of the breach by a systems management agency on May 28. It later confirmed that the access occurred on May 14.

The research institute said an investigation is under way after it reported the incident to the Ministry of Science and ICT and the National Cyber Security Center under the National Intelligence Service(NIS) on June 1.

It also blocked the 13 internet protocol(IP) addresses that conducted the attacks with firewalls and updated systems security.

The institute, however, declined to comment on whether the hacking attempt was made by the North or what documents were leaked.

The cyberattack came to light after main opposition People Power Party(PPP) Rep. Ha Tae-keung claimed earlier in the day that a hacker group under the North's reconnaissance general bureau, known as Kimsuky, committed some of the attacks.