Washington DC - The US is set to send controversial cluster munitions, which are banned by most countries, to Ukraine to help the war-torn nation in its efforts to repel Russia's invasion, according to multiple reports.

"I don't have anything to announce today," Pentagon spokesman Pat Ryder told reporters, but added: "In the event that we do provide this capability, we will be carefully selecting rounds with lower dud rates for which we have recent testing data."

US Chief of Staff Mark Milley had already indicated last week that Washington was considering the move. Ukraine has long called for the delivery of cluster munitions to help defend itself.

CNN said an official announcement could come on Friday.

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Cluster munitions are missiles and bombs that burst in the air over the target, scattering or releasing many small explosive devices known as submunitions.

Experts say a significant percentage of the explosive devices are duds that do not detonate but remain on site as dangerous unexploded ordnance, often killing civilians.

Over 120 countries have committed to banning the cluster munitions, but the US – which ravaged Laos with this type of weapon in the 1960s and 70s – along with Ukraine and Russia, have refused to do so.

The US says it has provided or pledged more than $40 billion in military aid to Kyiv since the war began in February 2022.