State-owned radio said police shot dead five gunmen after the weekend assault, as the bus was travelling through a communist stronghold during the Vietnam war.

It is not known who carried out the attack but reports said police believed the incident was motivated by what they termed a business conflict.

Correspondents say there have been several violent attacks in Laos this year.

Earlier this year, buses travelling between the capital, Vientiane, and a popular tourist destination, Luang Prabang, were attacked.