The UK is committed to a convention which “discourages” the use of cluster bombs, Rishi Sunak has said, after the US agreed to supply them to Ukraine.
The prime minister highlighted that the UK is one the countries to have banned the controversial weapons, which have a record of killing civilians.
But he also emphasised the government would continue to support Ukraine.
US President Joe Biden made what he called a “very difficult decision” to supply them to Kyiv on Friday.
Spain, one of 123 nations to ban cluster bombs, has criticised the decision to send them, which has also been condemned by human rights groups.
Cluster munitions are a method of dispersing large numbers of tiny bomblets from a rocket, missile or artillery shell that scatters them in mid-flight over a wide area.
They are meant to detonate on impact, but a significant proportion of them can fail to explode initially – often when they land on wet or soft ground. This means they can explode at a later date, killing or injuring people.
Neither the US, Ukraine or Russia are signatory to the international treaty – the Convention on Cluster Munitions – banning the use or stockpiling of them over the indiscriminate damage they can inflict on civilian populations.
Speaking to reporters in Selby, Yorkshire, on Saturday, Mr Sunak said the UK is “signatory to a convention which prohibits the production or use of cluster munitions and discourages their use”.
“We will continue to do our part to support Ukraine against Russia’s illegal and unprovoked invasion, but we’ve done that by providing heavy battle tanks and most recently long-range weapons, and hopefully all countries can continue to support Ukraine,” he added.
“Russia’s act of barbarism is causing untold suffering to millions of people.”
Mr Sunak is due to meet with Mr Biden in London on Monday, ahead of a Nato summit in the Lithuanian capital Vilnius on Tuesday.
Rishi Sunak spoke carefully when asked for his response to the US now giving cluster munition to Ukraine.
He didn’t criticise the US’s decision but did point out that the Convention discourages use of the bombs.
The UK is the second largest provider of military assistance to Ukraine – only behind the US.
As the conflict in Ukraine evolves, so too are the responses of Kyiv’s allies – on this issue the US and UK have gone in different directions.
Mr Biden justified supplying the weapons by saying the “Ukrainians are running out of ammunition”.
Speaking to CNN in an interview due to air on Sunday, he said it had taken “a while to be convinced” to make the “very difficult decision” to send them.
Ukrainian President Volodymyr Zelensky has hailed the “timely” move to deliver the bombs.
Ukraine’s Defence Minister Oleksii Reznikov said his troops would not use them in urban areas to avoid risking civilian lives, adding “these are our people, they are Ukrainians we have a duty to protect”.
But Spanish Defence Minister Margarita Robles has said her government’s position is that cluster bombs should not be used for the “legitimate defence of Ukraine”.
Germany, which has also signed the convention, said it would not provide them to Ukraine but that it understands the American position.
Human Rights Watch said both sides had used the weapons in the war, causing “numerous deaths and serious injuries to civilians”.
These comments were echoed by Amnesty International, who said cluster munitions pose “a grave threat to civilian lives, even long after the conflict has ended”.
The UN human rights office has also been critical, calling for their use to “stop immediately”.
Nato Secretary General Jens Stoltenberg has said the military alliance takes no position on cluster munitions.
Tobias Ellwood, the chairman of the UK’s defence select committee, urged the US to “reconsider” its decision – which he said was the “wrong call and will alienate international goodwill”.
“Their use leaves deadly unexploded ordnance over the battlefield, killing and injuring civilians long after the war is over,” the Conservative MP added.
Russia described the US decision as an “act of desperation” in the face of the “failure of the much-touted Ukrainian counteroffensive”.