Organizers said 88 countries were expected to sign on Wednesday and around 100 out of the world's 192 U.N. member nations will have signed by Thursday.
Cluster bomblets are packed by the hundreds into artillery shells, bombs or missiles that scatter them over vast areas. Some fail to explode immediately. The unexploded bomblets can then lie dormant for years until they are disturbed, often by children attracted by their small size and bright colors.
"Banning cluster bombs took too long. Too many people lost arms and legs," Norwegian Prime Minister Jens Stoltenberg said as he opened the conference.
Washington, Moscow and other non-signers say cluster bombs have legitimate military uses such as repelling advancing troop columns. But according to the group Handicap International, 98 percent of cluster-bomb victims are civilians, and 27 percent are children.
The Bush administration has said that a comprehensive ban would hurt world security and endanger U.S. military cooperation on humanitarian work with countries that sign the accord.
Activists said ahead of the signing that they hope the treaty will nonetheless shame non-signers into shelving the weapons, as many did with land mines after a 1997 treaty banning them.
"Once you get half the world on board, its hard to ignore a ban," said Australian anti-cluster bomb campaigner Daniel Barty. "One of the things that really worked well with the land-mine treaty was stigmatization. No one really uses land mines," he said.
The anti-cluster bomb campaign gathered momentum after Israel's monthlong war against Hezbollah in 2006, when it scattered up to 4 million bomblets across Lebanon, according to U.N. figures.
"In southern Lebanon, for more than two years, children and the elderly have been victimized (by cluster munitions)," Lebanese Foreign Minister Fawzi Saloukh said.
Norway called a conference to ban cluster bombs in February 2007. In May, more than 100 countries agreed to ban cluster bombs within eight years.
The treaty must be ratified by 30 countries before it takes effect.
"I think it's awesome that 100 countries are coming to Oslo to sign (the new cluster bomb treaty)," said American Jody Williams, who won the 1997 Nobel Peace Prize for her efforts to ban land mines.
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