Rishi Sunak has said the UK “discourages” the use of cluster bombs after the US agreed to send them to Ukraine.
President Joe Biden has faced criticism for supplying the munitions, which are banned by many allies because of their track record of killing and maiming civilians.
The prime minister said the UK was one of 123 countries that signed a convention banning their use, and would continue focusing on supplying tanks and long-range weapons to help the fight against Russia.
He added: “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.
“Russia’s act of barbarism is causing untold suffering to millions of people.
“It’s right that we collectively stand up to it.”
Mr Sunak will meet Mr Biden in London on Monday ahead of a NATO summit.
Why cluster bombs decision is controversial
Cluster bombs detonate in the air and release “bomblets” that scatter over a large area.
Opponents say they kill indiscriminately and that some of the smaller munitions can fail to detonate, posing a long-term risk to civilians.
Mr Biden has called it a “difficult decision” but said he had to act as “the Ukrainians are running out of ammunition”.
The US says Kyiv has provided assurances it will not use cluster bombs in urban areas, but some NATO allies are likely to be uneasy over their supply.
@Sky News