Viengkeo Kavongsone had lived in fear of such a catastrophe all his life - in the jungle, in the paddy fields, on the mountain - but never in his own back yard. It was late afternoon when it happened, and his wife, Van, and three young children were at home in their village in the province of Xieng Khouang in northern Laos. They were clearing the ditch that drains rainwater from their little wooden house.

The tin shovel scraped upon something hard and metallic - and that was the last thing they recalled.

The explosion peppered shrapnel into the legs of Van and her six-year-old daughter, Phetsida. The oldest boy, Soulideth, took the blast in the face and may lose his sight. Closest to the explosion was the youngest boy, Bounma. “He was the littlest,” his father said as he stood by the hospital beds of his wife and surviving children, “and he was right next to it.” The blast threw the child six metres (20ft) out of the ditch, and he died immediately - the latest victim of a spectral war that came to an end a generation before he was born.

The South-East Asian nation of Laos is not a country in conflict - in fact few places in the world are so torpid and peaceful. The weapon that killed Bounma was a tennis ball-sized pod of ball bearings that fell to earth when Lyndon Johnson was US President and the Beatles were at the height of their powers.

It was part of a cluster bomb - one of the most stubborn, long-lasting and cruelly undiscriminating weapons of modern war - scattered by American B52 bombers in the so-called “Secret War” intended to drive back communist guerrillas and block supply lines for US enemies in Vietnam.

Cluster bombs consist of an outer casing that splits open to release as many as 700 individual “bomblets” designed to explode on impact, spreading blast and deadly fragments over soldiers and armoured vehicles in a 30 metre radius. But invariably, between 10 per cent and 40 per cent of the bomblets fail to detonate.

They are small, innocuous looking, and often colourful - almost as if designed to attract the attention of playful children. And like the bomblet that killed Bounma, they can lie in the ground for a generation until the chance touch of a spade or a curious hand triggers them into deadly life.

“I remember when the bombs fell,” said 54-year-old Mr Viengkeo, who was a teenager at the time. “I remember seeing them falling. I taught the children to be careful: ‘If you see something and you don't know what it is, leave it and tell an adult'. But I had no idea there was a bomb there all the time, under my home.”

Finally, the world has started to take notice of cluster bombs. Next month in Dublin, about a hundred governments will gather to finalise an international treaty to restrict their use.

Many governments, including the victorious communists who still govern Laos, are pressing for a complete ban. The world's biggest military powers, including Russia, China and the US, are refusing to take part in the negotiations. And then there are those governments, including Britain, that want to retain the right to use certain kinds of cluster bomb.

“We refer to cluster bombs as the weapon that never stops killing,” said Peter Herby, of the International Committee of the Red Cross, which is lobbying for an unconditional ban. “It's bad enough when civilians get caught up and injured in conflict. But for us it's repugnant when killing goes on for years and decades simply because of the wrong choice of weapon. In the end politicians have to decide that some weapons are beyond the pale.”

The first cluster bombs were dropped by the Luftwaffe on Grimsby in 1943, and since then they have been used in more than a dozen conflicts. The momentum for the present treaty negotiations gathered after 2006 when the Israeli army fired four million bomblets on to southern Lebanon, where they continue to cause civilian casualties. But no nation in the world has suffered more from cluster bombs than Laos.

Between 1964 and 1973, when the Secret War was abandoned, US aircraft flew 580,000 missions and dropped two million tonnes of bombs on Laos. These included 277 million cluster bomblets. Assuming a failure rate of 30 per cent, 84 million of these are still lying in the ground.

The best figure for casualties caused by cluster bombs is 4,847 since the end of the war, almost half of them children. Deadly explosives have become part of everyday life. In the town of Phonsavan there are fences made of shell casings. Unexploded bombs are forged into axes, sickles, cow bells, rice cookers, belt buckles, boats and ladders. One particular cluster bomb with a tripod-shaped fin is commonly fitted with a light bulb and used as a lamp.

“This familiarity is a real problem,” said Joe Pereira, a British occupational therapist whose charity, Cope, supplies prosthetic limbs to victims. “People grow up with bombs in their houses and so when they see them in the forest they don't appreciate the danger.”

Battle lines drawn

— About a hundred countries will meet in Dublin next month to negotiate the last details of a draft treaty on cluster bombs. The biggest military powers, including the US, Russia, China, Pakistan and India, are not taking part

— Britain wants the term “cluster bomb” to be defined as a device with ten or more “bomblets” - which would allow it to continue using the M73 bomb, with only nine

— Britain also argues for exemption of the M85 because of its “self-deactivation device”. Such “smart cluster bombs” are said to have a failure rate of 1 per cent, but when used by Israel in Lebanon in 2006, up to 10 per cent failed to explode or deactivate

— Other controversies focus on the amount of time countries would be given to stop using cluster bombs, and over military co-operation between states that had signed a treaty and those that had not

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