Computer networks of South Korea's key broadcasters have come under cyber attack in what Seoul suspects is a Pyongyang-orchestrated cyber-attack.

Broadcasters KBS, MBC and the YTN have been "entirely halted," the media organisations have told the police, the Yonhap news agency has reported

Networks of banks have also been paralysed by the latest outrage.

Seoul officials are probing whether North Korea is behind the widescale attack although the exact source has yet to be found.

"Reports have been made simultaneously so we have dispatched investigators to the scene," said a Seoul security official familiar with the matter.

North Korea has been accused of launching a cyber war against South Korea. Hackers from the secretive state have been trying to infiltrate Seoul's information system to steal military secrets, it is claimed.

"North Korea is attempting to use hackers to infiltrate our military's information system to steal military secrets and to incapacitate the defence information system.The military is updating the information protection policies and systems as part of the efforts to strengthen its response capabilities," Seoul's Defence Security Command Army Lieutenant General Bae Deag-sig told the Korea Herald earlier.

In June last year, North Korea was accused of jamming the South's flight signals for over a month.