The incident took place about 8 am on Sunday in Xaysomboun (pronounced Sai-sum-boon) when the victims were riding in a vehicle Xinhua reported.

The mountainous province has seen an increase in violence in recent months. In the years past it was the scene of clashes between government forces and the Hmong ethnic minority.

“Laos military personnel rushed to the scene and the injuredsurnamed Zhou has been shifted to a hospital in the capital Vientiane for treatment” said the news agency.

One of the casualties worked for a mining company based in southern China’s Yunnan province.

This is not the first time employees of Chinese companies have been killed abroad.

In May 2014 up to 16 Chinese workers were killed during anti-China riots in Vietnam. In November at least three executives of a Chinese state-run railway firm were killed in Mali when militants attacked a hotel.

It is unclear whether Sunday’s blast was part of a targeted attack on Chinese nationals in the country although Chinese embassy officials described it as a “suspected bomb attack” calling on local authorities to promptly investigate the incident.

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 state press provided any details.

The US Embassy in Laos in November prohibited its employees from traveling to Xaysomboon province due to what it described as night time 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.

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 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.

Laos suffers from unexploded ordnance an enduring problem following the US’ carpet-bombing campaign in the communist nation during the Vietnam War.

On Monday US State Secretary John Kerry met with Laos’ Prime Minister Thongsing Thammavong to discuss the deadly legacy of unexploded explosives.

“We have been working on this project of clearing mines and undoing effects of war for a long time and it continues” Kerry said before meeting with the prime minister.

More than two million tons of munitions were dropped during half a million bombing missions. Some 30% of the devices failed to detonate leaving around 50000 people dead since the end of the war.