Japanese Prime Minister Yukio Hatoyama on Monday expressed regret over the death of a Japanese journalist during Saturday's clashes in Bangkok and urged the Thai government to investigate the case.

The prime minister also said he has called on Thailand to make further efforts to ensure the safety of Japanese nationals in the country and stop the domestic chaos as soon as it could.

Hiroyuki Muramoto, a TV cameraman for Reuters news agency's Tokyo bureau, was killed apparently from a gunshot during clashes between antigovernment protesters and security forces in Bangkok on Saturday.

"It's very regrettable that Mr. Muramoto died," Hatoyama told reporters in Tokyo before heading for Washington to attend the U.S. -sponsored Nuclear Security Summit. "I requested (the Thai government) to adequately investigate the cause (of the death)."

In a personal letter sent to Hatoyama on Sunday, Thai Prime Minister Prime Abhisit Vejjajiva pledged to implement a thorough probe into the cause of Muramoto's death, Kyodo News reported.