On the 500th day of the Ukraine war, the US and UK are divided over whether it's right to send cluster bombs to the battlefield, ITV News' Tom Sheldrick reports
The Prime Minister highlighted the UK was one of 123 signatories of a convention banning their use after the US leader made the “difficult decision”.
Mr Sunak, who will be meeting Mr Biden in London on Monday ahead of a Nato summit, said Britain was instead supporting Kyiv by providing tanks and long-range weapons.
Earlier, Mr Biden said he stood by the decision to send cluster munitions to Ukraine, describing the controversial step as a temporary measure to help Kyiv halt Russian tanks.
The leader defended the controversial move to send the munitions, which are banned by most other countries around the world, including the UK, to aid America's ally.
It is the latest round of weaponry promised to Ukraine in its fight against Russia's invasion.
Mr Biden decided to provide cluster munitions to Ukraine for its war against Russia, even though the United Nations (UN) has urged the warring countries to avoid using them.
An exclusive interview with Mr Biden over the munitions controversy is set to air on CNN on Sunday afternoon, UK time.
The first glimpse of Biden's exclusive interview with CNN over the cluster munitions controversy
In the first clips from the interview, released ahead of its broadcast, the leader tells CNN’s Fareed Zakaria it was a “difficult decision” to provide Ukraine with the munitions, but he was ultimately convinced Kyiv needed the ammunition for its counteroffensive against Russia.
He also described the delivery as a 'temporary' measure to deal with ammunition shortages on the Ukraine frontlines, in a bid to halt Russian tanks.
“This is a war relating to munitions. And they’re running out of that ammunition, and we’re low on it,” Mr Biden told the programme.
“And so, what I finally did, I took the recommendation of the Defense Department to – not permanently – but to allow for this transition period, while we get more 155 weapons, these shells, for the Ukrainians.”
He also acknowledged that more than 100 nations, including the UK, have outlawed cluster munitions.
The US and Ukraine are not signatories to the convention banning the munitions, which have been used extensively by Russia in the conflict.
"It was not an easy decision,” Mr Biden said. “We’re not signatories to that agreement, but it took me a while to be convinced to do it.”
He added: “But the main thing is they either have the weapons to stop the Russians now – keep them from stopping the Ukrainian offensive through these areas – or they don’t. And I think they needed them.”The interview will air in full on “Fareed Zakaria GPS” on Sunday afternoon, UK-time.
Mr Sunak chose not to back his counterpart's move during a by-election campaign stop to Selby on Saturday afternoon, pointing to the UK’s commitment 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.
“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 and I’ll be heading off to the Nato summit next week in Vilnius, where we will be discussing exactly this with our allies how we can strengthen our support for Ukraine.”
The US has argued that Kyiv has provided assurances it will not use cluster bombs in urban areas but some Nato allies are bound to be uneasy over their transfer.
On Friday, ITV News correspondent Robert Moore also grilled a top US official about America's decision, after it was met with criticism by the international community.
Moore challenged the Pentagon's chief spokesman, General Patrick Ryder, to justify the supply of the munitions, warning that the ordnance, which can lie undisturbed for years before maiming people long after a conflict has ended, will ultimately harm children in Ukraine.
Watch correspondent Robert Moore's full interview with General Ryder
What is a cluster bomb?
Cluster bombs open in the air and release a wave of smaller bomblets to hit multiple targets at once.
The munitions have a track record for causing many civilian casualties, and hidden unexploded ordnance causes traumas years- even decades- down the track, long after a conflict has ended.
Cluster bombs have been kill and maim civilians in conflicts around the world, including Syria, Libya and Ukraine, often leaving victims who survive their explosion with life-changing injuries.
The Pentagon says the munitions it will provide to Ukraine have a reduced “dud rate.”
That means fewer of the unexploded rounds that can result in unintended civilian deaths. But critics say the collateral damage is unacceptable.
Colin Kahl, the under secretary of defense for policy, said the US will give Ukraine the most modern cluster munitions available, which have far lower dud rates.
He said the bombs have been tested five times between 1998 and 2020, and the US is confident the rate of unexploded duds is below 2.35 percent.
While he declined to say how many the US will send now, he said it has “hundreds of thousands” of cluster munitions available for Ukraine at the low dud rate.
According to the International Committee of the Red Cross, some cluster munitions leave behind bomblets that have a high rate of failure to explode — up to 40% in some cases.
A convention banning the use of cluster bombs has been joined by more than 120 countries that agreed not to use, produce, transfer or stockpile the weapons and to clear them after they’ve been used.
The UK is among the key signatories and campaigners on outlawing the use of cluster munitions, and actively invests in the clearance of cluster munitions, anti-personnel mines, and other explosive remnants of war around the world.
The United States, Russia and Ukraine are among those who have not signed on to the convention.
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