North Korean scientists and technicians have been scrambling to boost the country's nuclear capabilities ahead of a major party congress in May, causing key military secrets to be exposed, intelligence authorities here said Sunday.

Since mid-February, all sectors of North Korean society have engaged in a "70-day battle" to prepare for the first Workers' Party Congress in more than three decades. As part of that campaign, scientists and technicians have been disclosing what they claim to be achievements in the North's nuclear technology to show loyalty to leader Kim Jong-un, according to the sources.

"It appears that the level of nuclear and missile technology, and key military secrets are being exposed in the process," said one source who spoke on the condition of anonymity.

In recent weeks, the North has published photos of what appears to be a nuclear warhead detonator, a simulation of the re-entry of a nuclear warhead on a ballistic missile and strike plans of the strategic forces.

However, a careful analysis of the photos by South Korean and American experts revealed that such purported achievements were made in haste in order to be shown off to the public, another source said. 

"North Korea's scientists and technicians are overly exposing key secrets of their nuclear and missile technology," a government source said. "Although the North is boasting these technologies as cutting-edge or indigenous, South Korean and American experts in the nuclear and missile fields are looking into the exact level of the disclosed technology and how far it's expected to develop."

North Korea's nuclear and missile threats have grown since its fourth nuclear test in January and long-range rocket launch last month.

On Friday, the North fired two medium-range ballistic missiles off its east coast in defiance of U.N. resolutions banning such activity. (Yonhap)