At least 30 states have to ratify the treaty to bring it into effect
The first of more than 100 countries have begun signing a treaty to ban current designs of cluster bombs, at a conference in Oslo, Norway.
Campaigners are hailing the treaty as a major breakthrough.
But some of the biggest stockpilers, including the US, Russia and China, are not among the signatories.
First developed during World War II, cluster bombs contain a number of smaller bomblets designed to cover a large area and deter an advancing army.
But campaigners, including some in the military, have long argued they are outmoded and immoral because of the dangers posed to civilians from bombs that do not explode and litter the ground like landmines.
As he opened the signing convention in Oslo, Norwegian Prime Minister Jens Stoltenberg said the treaty would make the world safer, but had been too long in coming.
"Too many people lost their lives and their limbs; too many futures were shattered," he said.
"The tragedy of their needless suffering is matched only by our joy today in being able to prevent more human misery in the future."
Jakob Kellenberger, president of the International Red Cross, reminded the meeting of the deadly legacy of cluster bombs.
"The path to Oslo is also traced through the mountains and the rice paddies of south-east Asia where several hundred million sub-munitions were dropped and many tens of millions remain today," he said.
"This path runs through the lives of civilians in Laos, Cambodia and Vietnam who have lived with the threat of unexploded sub-munitions for four decades."
Archive footage of cluster bombs being dropped
The treaty, agreed in Dublin in May, will not ban cluster weapons outright, reports BBC defence and security correspondent Rob Watson.
It allows for the development of cluster bombs with greater precision and lower failure rates - an approach the US in particular says it is already pursuing.
As well as banning the current design of cluster bombs, the treaty also provides for clearance in those countries littered with unexploded bomblets.
Campaigners say that even big countries like the US and Russia that have not signed the treaty would not want to be stigmatised any more by links to cluster bombs.
Jody Williams, an anti-landmine campaigner and Nobel Peace Prize winner, said the US had "essentially obeyed" all the elements of the treaty and she hoped US President-elect Barack Obama would sign it.
"Mr Obama tells us to look for hope and change," she told Reuters news agency. "I like hope and change, but I want to see him sign it."
The treaty will come into effect six months after 30 states have ratified it and deposited the instruments with the UN, Reuters reported.
"We need 30 ratifications as soon as possible so that the obligations in this treaty will begin to bite," said Thomas Nash, co-ordinator of the London-based Cluster Munition Coalition.
Afghanistan signed the treaty on Wednesday - a move which surprised many who thought the country would bow to pressure from the US to refrain.
Soraj Ghulan Habib, a teenage victim who lost his legs in a cluster bomb explosion seven years ago, said he had lobbied Afghanistan's ambassador to Norway to sign the treaty.
He told AP: "Today is an historic day."
The signing convention in Oslo is due to last two days, with organisers expecting 88 countries to sign on Wednesday, and a further 22 signing on Thursday, Associated Press reported.
The treaty will then go to UN headquarters in New York where more of the 192 member states will be able to sign.
HOW A CLUSTER BOMB WORKS
1. The cluster bomb, in this case a CBU-87, is dropped from a plane and can fly about nine miles before releasing its load of about 200 bomblets. 2. The canister starts to spin and opens at an altitude between 1,000m and 100m, spraying the bomblets across a wide area. 3. Each bomblet is the size of a soft drink can and contains hundreds of metal pieces. When it explodes, it can cause deadly injuries up to 25m away.
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