XIENG KHOUANG, Laos - Laotian children chase each other through their school playing field, unaware of the 248 unexploded bombs buried a few steps away -- the lethal legacy of a war that ended three decades ago.

Remnants of the Vietnam War which ended in 1975 litter this tiny Southeast Asian nation, which became the most bombed country in the world after US forces dropped planeloads of ordnance to cut off Northern Vietnamese supply routes.

Cluster bombs and other munitions rained down on more than 87,000 square kilometres (33,590 square miles) of Laos, but nearly a third failed to explode as they fell on boggy rice paddies and forests.

Authorities in Laos, which has a total population of 6.7 million, estimate that since the war ended 10,500 people have been killed and 11,500 wounded by these leftover bombs -- roughly equivalent to one person every day.

Staff and the 132 pupils at Tontai school in northeastern Xieng Khouang province, one of the worst hit areas, have lived with the daily fear of such incidents for years.

Xiang Khouang, in the country's northeast, is an eight-hour drive over mountainous roads from the capital Vientiane, and was the second most bombed province in Laos during the war, with an estimated 63,000 munitions deployed.

In Tontai village, where just 220 people live, four explosions have already killed one person and injured five.

"I was surprised they built the school here," said Sithat Sitavang Sent, a mine clearer sent to rid the area of ordnance. "But the village has no choice, they have to, even though they know there are unexploded bombs around."

A mine clearance team has cleared 4,000 square metres (43,055 square feet) of land in Tontai and uncovered 3,900 cluster bomblets buried underground, including 248 in the field adjoining the school.

The proportion of children killed by cluster bombs has risen to 50 percent over the last decade, as curiosity and the hope of making a few dollars from scrap metal make them more vulnerable, according to UXO Lao, the government agency dealing with unexploded ordnance.

Rising metal prices now mean one kilo of scrap could fetch up to three dollars at the local foundry -- a substantial sum in a country where 40 percent are malnourished and just under half have no access to clean water, according to UN figures.

Children come across the bombs lying in playing fields and rice paddies. "They are about the size of a D-cell battery and have a ribbon hanging from them that just makes a kid want to go and pick it up and twirl it around with their fingers too -- which will arm it and function it very quickly," said Mark Hiznay, a researcher for New York-based Human Rights Watch.

In an attempt to stop the rising numbers of children being injured or killed, teachers are now sent to schools in a joint enterprise between the Laos government and humanitarian organisations.

They visit and lecture elementary school students on the dangers of cluster munitions, before getting them to act out plays, song and dance, and puppet shows for each other.

For some, at least, it is working.

"If I see UXO (unexploded ordnance) I will inform the village chief and ask him to tell UXO Lao to come and destroy it," said eight-year-old Sonexny at a school in Xiang Khouang.

His teacher, Monesy Bounmaksidavong, said the lessons are aimed at ears beyond the classroom.

"I can see their behaviour has changed," said Monesy. "They promise they will explain to their parents and their friends who weren't at the meeting about the danger of UXO."

This education and mine clearance work will ramp up with the help of a new international treaty being signed in Oslo, Norway, on December 3.

The treaty bans the use, stockpiling and trade of cluster munitions, but more importantly for the people of Laos it provides for the clearance of contaminated land within ten years.

That target may prove too ambitious for a country such as Laos where up to a quarter of the country's 10,000 villages are still blighted -- their young victims still tragically linked to the old dogs of war.