Japanese broadcaster TV Asahi apologised Saturday after its Bangkok bureau chief posted an image of his genitals on a mobile forum set up by Thailand's foreign ministry, which warned of "consequences".

A spokesman for the channel said the unnamed employee had been removed from the job due to his "extremely inappropriate" behaviour.

The ministry demanded an explanation for the graphic picture that appeared late Monday in the forum, which was set up for foreign journalists working in Thailand.

"We deeply apologise to the Thai foreign ministry and other people concerned," the spokesman said, adding the journalist had been urged to "seriously reflect" on the incident.

Japanese media said the bureau chief, who is in his forties, had meant to send the picture to a female friend, but instead uploaded it through popular messaging app Line to about 150 journalists who belong to the forum.

He left the forum immediately after the incident, prompting a warning that "actions will be taken" from a ministry official and a vomiting emoji from one group member as a few others in the forum questioned what had just happened.

"May we remind you that this (forum) is for official purposes. Actions will be taken," the ministry official said.

"Just leaving the room does not mean this action won't have consequences."

Cases of so-called "sexting," or sending sexually explicit images by phone, have exploded with the prevalence of smartphones and other mobile devices.

In one of the best known incidents, Anthony Weiner quit the US House of Representatives in 2011 after confessing that he used social media to send sexually explicit pictures of himself to a number of women.

His sexting problems returned and foiled his chances in New York City's mayoral race two years later.