In her letter to the US government, Alice Jill Edwards, a UN Special Rapporteur, said that cluster munitions "indiscriminately and seriously injure civilians both at the time of use and in post-conflict" and should not be used.
"I respectfully urge Your Excellency's Government to reconsider the decision to transfer cluster munitions and to halt any plan towards the implementation of such decision," Edwards, the special rapporteur on torture and other cruel, inhuman or degrading treatment or punishment, wrote in the letter.
The publication of the letter, dated July 14, comes days after US officials said the administration of US President Joe Biden was close to approving the shipment of longer-range missiles packed with cluster bombs to Ukraine to give its forces the ability to cause significant damage deeper within Russian-occupied territory.
Cluster munitions are prohibited by more than 100 countries.
Russia, Ukraine and the United States have not signed the Convention on Cluster Munitions which bans production, stockpiling, use and transfer of the weapons.
They typically release large numbers of smaller bomblets that can kill indiscriminately over a wide area.
Those that fail to explode pose a danger long after a conflict ends.
"Women, children and the elderly are most likely to be killed in indiscriminate attacks against civilian populations," Edwards said in a statement accompanying her letter.
"With cluster munitions, this is an enduring threat as they often fail to explode as intended on impact and can remain dangerous for decades."
