The US is set to approve sending cluster munitions to Ukraine to help Kyiv as it attempts to gain ground in a counter-offensive against Russia.
Critics are angry over the decision by President Joe Biden's administration, saying the bombs kill civilians long after a conflict ends.
Supporters say the weapons are needed to counter Russia, which is also using cluster munitions.
A convention banning the use of cluster bombs has been joined by more than 120 countries but the US, Russia, Ukraine and scores of other countries are not part of it.
Here is a look at what cluster munitions are, where they have been used and why Washington plans to give them to Kyiv now:
What is a cluster munition?
Cluster munitions are bombs that explode above the ground and then release dozens or hundreds of smaller submunitions, or bomblets, that scatter across a wide area. These smaller bombs are designed to attack tanks, equipment and troops at the same time.
The munitions are launched by the same artillery weapons that the US and allies have already provided to Ukraine for the war – such as howitzers – and the type of cluster munition that the US is planning to send is based on a common 155mm shell that is already widely in use across the battlefield.
In previous conflicts, cluster munitions have had a high failure rate, which meant that thousands of unexploded bomblets remained behind and killed and maimed people decades later. Children often bear the brunt of the casualties, as they pick up unexploded bomblets while playing.
The US last used its cluster munitions in battle in Iraq in 2003, and decided not to continue using them as the conflict shifted to more urban environments with denser civilian populations.
Why provide them now?
For more than a year the US has dipped into its own stocks of traditional 155 howitzer munitions and sent more than two million rounds to Ukraine. Allies have provided hundreds of thousands more.
A 155mm round can strike targets 24 to 32 kilometres away, making them a munition of choice for Ukrainian ground troops trying to hit enemy targets from a distance. Ukrainian forces are burning through thousands of the rounds a day battling the Russians.
The cluster bomb is an attractive option because it would help Ukraine destroy more targets with fewer rounds, and because the US hasn’t used them in conflict since Iraq, it has large amounts of them in storage it can access quickly.
A letter written by top House and Senate Republicans in March, to the Biden administration, said America may have as many as three million cluster munitions available for use, and urged the White House to send some of these to alleviate pressure on US war supplies.
Is using them a war crime?
The use of cluster bombs itself does not breach international law, but using them against civilians can be a violation. As in any strike, determining a war crime requires looking at whether the target was legitimate and if precautions were taken to avoid civilian casualties.
“The part of international law where this starts playing [a role], though, is indiscriminate attacks targeting civilians,” Human Rights Watch’s associate arms director Mark Hiznay told the Associated Press.
“So that’s not necessarily related to the weapons, but the way the weapons are used.”