By Jonathan Head
Reports from Laos say at least 10 people were killed after gunmen opened fire on a bus travelling between the tourist resort of Luang Prabang and the capital Vientiane.
It is the second such attack to take place in the same area this year.
The Lao authorities have given little information about either incident, but diplomatic sources say the attacks are believed to be the work of ethnic rebels who have maintained a low-level insurgency against the communist government over the past 30 years.
The habitual silence of the Lao government on the subject cannot disguise the fact that they have a serious security problem around their two most popular tourist destinations.
No foreigners appear to have been killed in this most recent bus ambush, but it is bound to damage confidence in the country's fast-growing tourist industry.
Like the attack in February, this one took place on the road between the old royal capital Luang Prabang and the town of Vang Vieng - both have become very popular with foreign travellers.
The government usually blames incidents like this on what it calls bandits, but the gunmen are widely believed to be from the ethnic Hmong minority, some of who have waged sporadic armed campaign against the government ever since the communists came to power in 1975.
Hmong exiles in the United States continue to complain of violent repression by the Lao security forces, but have so far attracted little international interest in their cause.
However, targeting the tourist industry may prove more effective - it provides one of the few sources of income to the rulers of one of the world's poorest and most isolated countries.