North Korea has sought to develop nuclear weapons since the 1960s.

Diplomatic documents from Russia and Hungary released Wednesday said the North asked the Soviet Union for a nuclear missile in 1963, seeking nuclear technology from foreign nations.

The North also claimed that it had nuclear weapons from the 1970s.

One document quoted a North Korean embassy official in Hungary as saying in February 1976 that Pyongyang had completed war preparations and was ready to use nuclear instead of conventional weapons if a war broke out on the Korean Peninsula.