Radio Free Asia, which is financed by the United States government, reported on Thursday that the attack had taken place at a road construction site and that work on the project stopped afterward. The blast was the third in the area in a month, the report said, and soldiers defused a roadside bomb in the area on Dec. 30.

One witness reported driving past the bomb site shortly after the attack and seeing about 10 soldiers inspecting a damaged truck with the dead and wounded Chinese inside, Radio Free Asia said. The report also quoted an official with the road construction company saying it was removing its equipment from the construction zone.

Hua Chunying, a Chinese Foreign Ministry spokeswoman, said in a regularly scheduled news conference in Beijing on Monday that consular officials from the embassy in Vientiane had visited with the wounded person, and that China had urged the Laotian government to solve the case as soon as possible. The ministry also advised Chinese citizens in Laos to take more precautions. Ms. Hua did not offer any potential motives for the attack.

China is one of the biggest trade partners and foreign investors in Laos, a landlocked country ruled by the Lao People’s Revolutionary Party, which is Communist. A growing number of Chinese businesspeople are working in Laos, and that has led to resentment among some Laotians.

One signature investment project by China is a 260-mile China-Laos railway that is expected to cost more than $6 billion and that will connect Vientiane with Chinese cities. China has a 70 percent stake in the project, which officials say will be in operation by 2020. China’s long-term goal is for the train to connect Kunming, in Yunnan Province, with Singapore, which is far south of Laos.