The cyber intruders claimed to belong to a hacking activist group called Anonymous, Yonhap News Agency reported. The attacks at the presidential office and the Office of the Government Policy Coordination reportedly occurred about 9:30 a.m., and both websites were closed for repair.
Yonhap said immediately after the hacking at the presidential office, its website displayed messages in red. One read "Great leader Kim Jong Un," who is the leader of North Korea.
Another read: "We Are Anonymous. We Are Legion. We Do Not Forgive. We Do Not Forget. Expect Us," and carried a photograph of South Korean President Park Geun-hye.
The Wall Street Journal reported the presidential office's website remained unavailable until midday Tuesday. It said websites of the prime minister's office and national tax agency also could not be accessed.
Similar cyberattacks March 20 affected six South Korean banks and broadcasters. North Korea was blamed for those attacks but it denied any involvement.