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 of 123 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 the 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 do not 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 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.
Mr Biden justified supplying the weapons by saying the “Ukrainians are running out of ammunition”. Ukrainian President Volodymyr Zelensky has hailed the “timely” move to deliver the bombs.
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”.
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.
