BEIJING (AP) — Two Chinese citizens have been killed and one injured in a suspected bomb attack in central Laos, China's official Xinhua News Agency reported Monday, a mountainous area that in recent months has seen an increase in violence and in years past was the scene of clashes between government forces and the Hmong ethnic minority.

The incident took place about 8:00 a.m. on Sunday in the province of Xaysomboun (pronounced Sai-sum-boon) when the victims, one of whom was employed by a Chinese mining company, were riding in a vehicle, Xinhua reported.

Chinese diplomats have visited the survivor, identified by the surname Zhou, and have requested a swift investigation, Xinhua said. An official contacted at the Lao Embassy in Vietnam, the country's closest ally, said he was unaware of the report.

China is a major investor in Laos' rich abundance of minerals and other natural resources and shares its one-party form of authoritarian communist government. A special Chinese presidential envoy, Song Tao, is due to visit the country this week, Xinhua said.

Since November, there has been an increase in violence in the province, though the perpetrators have not been identified, nor has the tightly controlled state press provided any details.

In a notice posted on its website, the U.S. Embassy in Laos in November prohibited its employees from traveling to Xaysomboon province due to what it described as nighttime shooting attacks by unidentified assailants. It said one person was killed on Nov. 17 and another wounded on Nov. 18.

The Hmong fought on the side of a pro-American regime during the Vietnam War, and after the communist Pathet Lao took over in 1975, many fled abroad or hid in the jungle. Until a few years ago, there were several small bands of Hmong resisters who continued to hide in the jungle and occasionally clash with security forces, but most eventually surrendered.

The U.S. government-funded news service Radio Free Asia has reported additional attacks in November, December and January, citing unnamed police and other sources. In the latest reported attack, a bus came under fire on Jan. 14, leaving about a dozen passengers hurt but none killed, said RFA.

While RFA's reports could not be independently confirmed, it has a record of being well-informed about Laotian affairs.

In a report forwarded to The Associated Press earlier this month, Hmong sympathizers gave their own version of the recent violence, saying that from mid-November until the end of December, there had been six attacks by government forces on groups of Hmong, killing at least seven and wounding 21.

The report, which came from a source which has provided accurate information in the past, also said that 13 Hmong villagers had been arrested in November for contacting people in the jungle, meaning Hmong who are hiding from the authorities. The source declined to be named because of fears for his personal security.

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Associated Press Writer Grant Peck in Bangkok contributed to this report.