The British Government is accused of being the chief obstacle to the signing of a treaty to ban cluster bombs, which have maimed and killed thousands of civilians worldwide.

Countries that have suffered the impact of the bombs, humanitarian groups and former commanders of British forces have called for the UK to drop its insistence on retaining cluster munitions, a stance, they say, that is likely to scupper hopes of securing an agreement at an international conference starting in Dublin today.

More than 100 countries are taking part in the talks. Delegates will point out that the vast majority of cluster bomb victims are non-combatants. Opponents of the weapon received the backing yesterday of Pope Benedict XVI, who called for a "strong and credible" treaty to end their use.

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The two sets of weapons at the heart of the argument are the M85 and the M73, munitions fired, respectively, by artillery and rockets. British officials claim these are "smart" weapons which minimise the risk of "collateral damage" and are essential for military operations. The M85 is meant to self destruct and not pose a lingering threat to civilians. However, according to the United Nations, 300 civilians were killed or injured in Lebanon, where Israel used the weapons in 2006.

An Apache helicopter can launch 684 M73 bomblets in one attack. They were used by the Americans in the 2003 invasion of Iraq. Their use was criticised by US forces, who had to negotiate unexploded cluster munitions on their way to Baghdad. The first two British soldiers killed in Kosovo were casualties of Nato cluster bombs they had been trying to clear. Senior Foreign Office sources said the UK was not prepared to give up the M73 and the system was "non-negotiable". There was said to be flexibility over the M85, but the Ministry of Defence is expected to resist losing them.

The UK is said to be under strong pressure from the Americans – who are not taking part in the Dublin talks – to resist signing up to banning cluster bombs. Defence officials in London say a range of issues is at stake, including munitions stored at US bases in Britain, and the legal status of British soldiers serving alongside Americans where the US may use cluster weapons.

There are said to be divisions within the Government over the Dublin summit. Lord Malloch Brown, Foreign Office minister for Africa, Asia and the UN, is reported to have said he would be "uncomfortable" about a compromise that leaves some cluster bombs in the UK arsenal. The Environment Secretary, Hillary Benn, favours an overall ban.

Campaigners say the Government must live up to Gordon Brown's promise last year "to work internationally for a ban" on weapons that cause unacceptable harm to civilians. "Insisting on keeping some weapons and saying they are not negotiable is a deal breaker," said Simon Conway, a former British Army soldier who is director of the pressure group Landmine Action. "The position of the UK is a huge stumbling block to achieving a comprehensive treaty. Des Browne, the Defence Secretary, has told me himself that he did not believe the M73 was appropriate for counter-insurgency operations."

Lord Ramsbotham, a fomer British Army general and chief inspector of prisons, is among a number of distinguished senior officers, including General Sir Rupert Smith, General Patrick Cordingley and Field Marshal Lord Brammall, who have asked the Government to sign the treaty. Lord Ramsbotham, who flew to Afghanistan yesterday as part of a parliamentary delegation, said: "I am going to ask the commanders there whether they intend to use cluster weapons and I would be very surprised if the answer is 'yes'. There are moral objections to using cluster munitions, but tactical ones as well. They were designed to stop Soviet armour in the Cold War. There is no place for them in the type of warfare we are seeing now."