The UK government has sought fresh assurances from Saudi Arabia that British-made cluster bombs have not been used in the conflict in Yemen.
Amnesty International said it had documented the use of the weapons, manufactured in the 1970s.
Foreign Secretary Philip Hammond told MPs there was currently no evidence Saudi Arabia had used cluster bombs.
Mr Hammond said the weapons described were decades old and it was now illegal to supply such bombs under British law.
Answering an urgent question in the Commons, defence minister Philip Dunne said the UK had ratified the Convention on Cluster Munitions in 2010 and no longer supplied, manufactured or supported them.
He said there had been several conflicts in that region in the past decade so it was not clear that the evidence found had come from the current fighting.
Shadow defence secretary Emily Thornberry asked whether the Saudi military had used British planes to drop cluster bombs and what was the extent of British involvement in the conflict.
Mr Dunne replied: "I can categorically reassure [you] that no British planes have been involved in this coalition effort at all, let alone in dropping cluster munitions - that is the potential allegation. There is no British involvement in the coalition in targeting or weaponising aircraft to undertake missions."
Amnesty has written to Prime Minister David Cameron calling for a government inquiry into the allegations.
The human rights group claimed it found a partially-exploded BL-755 cluster bomb which had apparently malfunctioned, leaving scores of unexploded bomblets strewn over a wide area near a farm in Al-khadhra village, six miles from the Saudi border.
Amnesty said the bomb was originally manufactured by Bedfordshire company Hunting Engineering Ltd in the 1970s.
Amnesty International UK arms control director Oliver Sprague said: "Cluster bombs are one of the nastiest weapons in the history of warfare, rightly banned by more than 100 countries, so it's truly shocking that a British cluster munition has been dropped on a civilian area in Yemen."
Cluster bombs explained
- The Convention on Cluster Munitions prohibits all use, stockpiling, production and transfer of cluster bombs
- The convention has 108 signatories and became binding international law in 2010
- Cluster bombs pose particular risks to civilians because they release many small bomblets over a wide area
- During attacks, they are prone to indiscriminate effects especially in populated areas
- Unexploded bomblets can kill or maim civilians long after a conflict has ended, and are costly to locate and remove
Source: United Nations Office for Disarmament Affairs
A Saudi-led coalition of Arab air forces began carrying out airstrikes against Houthi rebels in Yemen last year.
The UN High Commissioner for Human Rights estimates that at least 3,200 civilians have been killed and 5,700 wounded, with 60% of the casualties caused by airstrikes, in that time.
The conflict between President Abdrabbuh Mansour Hadi's UN-recognised government and the rebels began in September 2014.