Newspapers in Japan and South Korea report that leader feared the reputation of his wife, Ri Sol-ju, might be damaged

North Korea has attacked the South's "reptile media" for running salacious reports alleging Kim Jong-un ordered nine performers to be executed to protect his wife's reputation.

Independent experts warn that rumours and deliberate misinformation about the regime are rife, partly because it is impossible to verify or disprove most stories about the tightly controlled country's elite. The editor of a Japanese magazine said a North Korean contact had told him of a mass execution in late August, possibly involving celebrities, but suggested that it could be related to other issues.

Ri Sol-ju was a singer with the Unhasu Orchestra before marrying the North Korean leader. Japan's Asahi Shimbun newspaper claimed at the weekend that members of that group and the Wangjaesan Art Troupe were executed because they were suspected of making a pornographic video and that Kim feared his wife's reputation might be damaged.

A similar story, published by South Korea's Chosun Ilbo a few weeks ago, did not mention Ri but claimed that a singer, Hyon Song-wol, rumoured to be Kim's ex-lover, was among a dozen performers executed for violating pornography laws.

Pyongyang's state news agency KCNA criticised media in the South for quoting the Asahi Shimbun story – without giving any details of the reports – saying it was an attempt to tarnish the leadership's image. It blamed "confrontation maniacs" for "[making their] servants of conservative media let loose a whole string of sophism intended to hatch all sorts of dastardly wicked plots and float misinformation".

John Delury, an expert on North Korea at Yonsei University in Seoul, noted numerous eye-catching stories in South Korean and Japanese media about the regime and particularly Kim that relied on an anonymous, single source, often from intelligence services.

"This stuff gets planted regularly in media outlets and then quickly goes viral," he said. "There's a global appetite for any North Korea story and the more salacious the better. Some of it is probably true – but a great deal of it is probably not.

"The normal standards of journalism are thrown out of the window because the attitude is: 'It's North Korea – no one knows what's going on in there.'"

The Asahi Shimbun report said it was based on information from a high-ranking defector, although it did not appear that the individual had spoken directly to the newspaper.

Leonid Petrov, a North Korea specialist at the Australian National University, said he had not heard of any high-level defections since 1997 and that while there was now much more information on the lives of ordinary North Koreans, through defectors and people working abroad, there was very little knowledge about the elite.

He added: "Whether this [particular event] happened in August, or earlier, or it never happened … is it likely that such an ugly thing may happen in North Korea? Everyone would say yes. There are simply no checks on the totalitarian power of the leader," he said.

Jiro Ishimaru, editor of Asia Press – a magazine based in Osaka, Japan, which has a network of informants in the North – said: "One of our contacts in North Korea has confirmed that a mass execution took place on 20 August, but we've also heard about several sightings since then of Hyon Song-wol [Kim Jong-un's ex-girlfriend]."

Ishimaru, identifying his source only as a male who had made contact with the North Korean public security officials, said the regime might be using a crackdown on "obscene materials" launched by Kim in early June as a pretext for neutralising potential threats to his authority.

The possible cause of Kim's rumoured execution order is an unflattering 2010 documentary about him produced by the South Korean broadcaster KBS which has been copied and smuggled into North Korea from China. Ishimaru's source said he had watched the documentary in North Korea.

Kim may have ordered the confiscation of copies of the video under the guise of a crackdown on pornography, Ishimaru said. "If the documentary becomes widely available in North Korea it could cause huge problems for the regime," he said.

While Chosun Ilbo said those executed were well-known figures, the identities of most of those involved remain a mystery.

Ishimaru said his contact had been able to confirm the identities of only two people, believed to be celebrities, adding that neither was Hyon. "There is still a lot we don't know, such as why North Korean celebrities might have been targeted for political reasons," Ishimaru said. "But as far as we can tell this doesn't look like a straightforward campaign against pornography."

The Asahi Shimbun claimed that, according to the defector, North Korean security services had wiretapped conversations among the performers and overhead one saying that Ri had "played around" before she met Kim.

A website carrying footage of Unhasu Orchestra performances has been closed down and both groups have been disbanded, according to media reports in Japan and South Korea. "That suggests that something involving performers really has happened," Ishimaru said.