What are cluster munitions and what is so controversial about the US sending them to Ukraine?

US president Joe Biden has decided to provide Ukraine with ground-launched cluster munitions, causing widespread controversy.

The Pentagon says the munition will help Ukrainian forces fight their way through deep Russian defences while Nato nations ramp up ammunition production.

First used during the Second World War, cluster munitions were used by the US military in both Iraq and Afghanistan.

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Cluster bombs have also already been used in Ukraine by both sides.

The cluster munition is made up of a casing containing more than 80 bomblets which are ejected at a set point in the shell's trajectory.

Each bomblet is about the size of a hand grenade and has a shaped charge that can kill infantry, but also penetrate light-skinned vehicles and has a kill zone of around 10 sq metres.

As well as being deadly, the US Army says cluster munitions also help reduce the chances of counter-battery fire because they destroy targets faster, allowing the gun crew to move before their location is triangulated by the enemy.

Due to their ongoing counter-offensive against the invading Russian forces, the Ukrainian Armed Forces and its Western backers are running out of artillery ammunition.

The counter-offensive is consuming huge amounts of ammunition, up to 8,000 shells a day, increasing the need for cluster munition.

A study conducted by the US Army found that cluster bombs were four times as effective as single shells, particularly against dug-in troops.

However, some Nato allies have expressed concern about the plans for America to supply cluster munition to Ukraine.

Prime Minister Rishi Sunak has made it clear that Britain "discourages" the use of cluster munitions as the UK is one of 123 signatories of a convention banning their use.

The Convention on Cluster Munitions prohibits the use or stockpiling of cluster munitions due to their indiscriminate effect on civilian populations. Unexploded bomblets continue to pose a threat to civilians long after conflicts end.