South Korea has not ruled out the involvement of North Korea in a cyberattack on the country's nuclear power plant operator and has requested the United States to help in investigations, an official involved in the proceedings said on Tuesday.
Korea Hydro and Nuclear Power Co Ltd (KHNP), which runs South Korea's 23 nuclear power reactors, said on Monday that its computer systems had been hacked but only non-critical data had been stolen. Operations were not at risk, it said.
The official at the joint investigation department of the Seoul prosecutors' office said the hacking bore some similarities to previous cyberattacks in which North Korea has been involved.
"We cannot rule out or confirm North Korea's involvement now, given the similirity of malignant codes patterns, and its verification will take some time," he said. "We don't (rule out North Korea's involvement). However, we cannot confirm it either."
The hacking has raised alarm in South Korea, which remains technically at war with the North. The incident comes as the United States has accused Pyongyang of a devastating cyberattack on Sony Pictures and has vowed to respond.
US help was being requested to investigate claims for the attack on the nuclear plant operator that have been posted on Twitter, the official in Seoul said.
"As Twitter's headquarters is based in the United States, we had to seek help from the United States for the probe," he said.
A Twitter user claimed responsibility for the attacks and demanding the shutdown of three aging nuclear reactors by Thursday. The post also asked for money in exchange for the leaked data.
The user, who was described in the post as chairman of an anti-nuclear group based in Hawaii, said more documents from the nuclear operator will be leaked if the reactors are not closed.
The nuclear operator and the government said only non-critical data was stolen by the hackers, and that there was no risk to nuclear installations. They also said it was confident that its nuclear plants could block any infiltration by cyber attackers that could compromise the safety of the reactors.
In 2013, South Korea accused the North of a series of cyberattacks on banks and broadcasters. Anti-nuclear activists in South Korea have also protested against the use of nuclear power.