North Korea has hacked South Korea's military cyber command, Seoul has alleged.

Pyongyang, which is believed to employ thousands of people in cyber warfare, has been accused of hacking into banks and media outlets in the South before, but never the military.

Classified information is thought to have been hacked, South Korean officials said on Tuesday, but it is not yet clear exactly what data was accessed.

“It seems the intranet server of the cyber command has been contaminated with malware. We found that some military documents, including confidential information, have been hacked,” a military spokesman told South Korea’s Yonhap News Agency.

It is not clear whether war plans were included in the haul taken by the North, which has in the past rejected allegations of involvement in cyber crime.

South Korea’s military said the compromised section of its network was isolated once the attack was detected.

The North has been focusing on application programming interfaces (APIs) since 2010, which can be designed to attack national infrastructures, North Korean defector and computer science professor Kim Heung-Kwang told the BBC.

The majority of alleged recent cyber attacks by the pariah state have focused on its neighbour the South, targeting government agencies, banks and media companies.

An apparent concerted campaign involving the planting of malicious code began in 2014, Reuters quoted police as saying.

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It was aimed at laying the groundwork for an attack on a massive scale, the agency said.

The campaign was discovered in February this year, when blueprints for the wings of F-15 fighter jets were found to be among the materials stolen.