Cluster munitions are designed to destroy multiple targets at once by dropping explosive “bomblets” over a wide area, risking potentially harming civilians or other unintended targets. Both sides are already actively using the weapons. Ukrainian cluster munitions killed at least eight civilians in Izium last year, according to Human Rights Watch.

Colin Kahl, the Pentagon’s undersecretary for defense policy, told reporters Friday that the U.S. will be providing Ukraine with its most modern cluster munitions with dud rates less than 2.35 percent, meaning the bombs are less likely to fail when deployed. The Pentagon also received written assurances from Kyiv that the bombs would not be used in urban areas populated by civilians, Kahl said.

“I’m as concerned about the humanitarian circumstance as anybody, but the worst thing for civilians in Ukraine is for Russia to win the war,” Kahl said.

The United States is not party to the 2010 Convention on Cluster Munitions, an international ban on their use signed by more than 100 countries.

“Russia started this unprovoked war against Ukraine,” Secretary of State Antony Blinken said in a statement. “Russia could end it at any time by withdrawing its forces from Ukraine and stopping its brutal attacks against Ukraine’s cities and people. Until Russia does so, the United States and our allies and partners will stand united with Ukraine, for as long as it takes.”

The munitions mark another instance of the U.S. eventually approving weaponry following repeated requests from Kyiv. Washington was previously hesitant about sending the cluster munitions due to the risk of civilian casualties and because of the rapid pace at which Ukraine has used weapons.

“Cluster munitions are among the most harmful weapons to civilians, as they disperse bomblets indiscriminately across a wide area that often fail to explode on initial impact, leaving duds that litter communities and endanger civilians, especially children, decades after a conflict ends,” the U.S. Cluster Munition Coalition, an organization that supports a comprehensive ban on U.S. cluster bombs, wrote in a statement on Friday.

“The argument I’m making is that Russia has already spread tens of millions of these bomblets across Ukrainian territory,” Sullivan said. “So we have to ask ourselves, is Ukraine’s use of cluster munitions on that same land actually that much of an addition of civilian harm, given that that area is going to have to be demined regardless?”