The Biden administration approved the transfer of cluster munitions to Ukraine on Friday, sparking concern from human rights groups and some congressional lawmakers over the weapon’s ability to harm civilians and children long after the bombs have fallen.

Cluster munitions are dropped by aircraft or fired by a ground-based weapons system over a target area, spreading out a few dozen to hundreds of submunitions. The weapons are valued militarily because they can strike multiple targets. 

But the weapons are banned by more than 100 countries because the submunitions spread out imprecisely, often fail to detonate and remain as explosive hazards for decades.

Washington’s green light to deliver the cluster munitions to Kyiv comes as Ukrainian forces are expending high rates of ammunition and are making slow progress in the counteroffensive that began last month.

Under Secretary of Defense for Policy Colin Kahl said the U.S. bomblets would “keep Ukraine in the fight” as they work through dug-in Russian defenses, which he described as “hard sledding.”