Labour’s Rachel Reeves has said she is concerned about US plans to arm Ukraine with cluster munitions.
The shadow chancellor said cluster bombs are not “appropriate weapons” to send to Ukraine.
US president Joe Biden has committed to sending Kyiv the weapons, despite many Nato allies prohibiting their use.
I would like to find a way to properly arm Ukraine but without using these weapons which can have an impact, not just on the battlefield that time, on that day, but for months and years afterwards— Rachel Reeves
Rishi Sunak did not express support for the move ahead of President Biden’s visit to the UK.
He said Britain “discourages” the weapons as one of the 123 signatories of a convention banning the bombs for their devastating impact on civilians.
Asked about President Biden’s commitment by the Sophy Ridge On Sunday programme on Sky News, Ms Reeves said: “We all agree that Ukraine needs to be properly armed to fight Russia and their illegal invasion.
“But I am concerned about the use of cluster bombs, and it is not just the UK who has these concerns, other countries clearly do as well.
“So I would like to find a way to properly arm Ukraine but without using these weapons which can have an impact, not just on the battlefield that time, on that day, but for months and years afterwards.
“That is something that causes me deep concern, and many other people as well.
“While I support President Biden’s desire to ensure Ukraine is fully armed to fight Russia, I am not convinced that these are the appropriate weapons.”
Mr Biden has said it was a “difficult decision” to send cluster bombs to Ukraine and sought to justify the move as needed to fortify Kyiv’s depleting ammunition stocks.
But the Prime Minister has said the UK is committed to the Convention on Cluster Munitions.
“Well, the UK is signatory to a convention which prohibits the production or use of cluster munitions and discourages their use,” he told broadcasters.
Cluster munitions deploy a large number of bomblets across a wide area.
Unexploded bomblets can continue to pose a threat to civilians long after conflicts end.
The Convention on Cluster Munitions prohibits their use or stockpiling because of their indiscriminate effect on civilian populations.
The US, Ukraine and Russia are not signatories.
Lord Ricketts, who served as the UK’s first national security adviser, told Sky News: “You can feel the allies are all very uncomfortable with this.
“We have all of us, apart from the Americans, signed up to the convention which means we don’t produce or stockpile or use these weapons. They are indiscriminate weapons, of course.”
The former senior diplomat added: “I think we do owe it to the Ukrainians to understand why they need these weapons.
“This offensive that they have launched, there is a lot riding on it. If it stagnates, bogs down, the risk is this war will just continue.”
Mr Biden will meet Mr Sunak on Monday, before the two leaders attend a summit in Lithuania on Tuesday where they will discuss support for Ukraine and its future membership of Nato.
The president will also meet the King at Windsor Castle.