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War in Ukraine is already horrific. The U.S. is set to make it worse.

Cluster bombs are illegal under international law, pose a long-term threat to civilians, and may be the next American weapon delivered to Kyiv.

The U.S. has been providing a steady flow of arms and other military support to Ukraine since Russia invaded in February 2022. But the U.S. is expected to announce Friday that it will, for the first time, send cluster munitions to Kyiv. Sending such weapons will not only undercut much of the moral high ground the West has taken in the conflict, but it will also threaten the safety of Ukrainian civilians. Those costs would make any victory against dug-in Russian forces a pyrrhic one.

Created during World War II, cluster munitions essentially break apart into many smaller bombs — also known as submunitions, or “bomblets” — in flight. That signature trait, and the fact that Kyiv is requesting the kind that can be used with howitzers or other ground-based rocket launchers, makes them particularly useful in Ukraine. A former commanding general of U.S. Army Europe told The Economist that “cluster munitions could suppress Russian fire from trenches and artillery, giving Ukraine more time to clear a path through minefields.”

The very thing that makes cluster munitions so effective makes them a long-term threat where they’re used.

But the very thing that makes cluster munitions so effective makes them a long-term threat where they’re used. American arms makers are required to ensure that fewer than 1% of their bomblets remain unexploded before hitting the ground. But those that do remain can function essentially as land mines, injuring or killing civilians who encounter them.

CNN reported in December that the U.S. was weighing a request from Ukraine to provide cluster munitions. It was only in recent weeks that the Pentagon began to hint that a decision was coming, including in testimony before Congress last month.

But even though the U.S. hasn’t yet provided such weapons to Ukraine, Ukraine has still been using them. Kyiv and Moscow had substantial stockpiles of them at the beginning of the war, and Russia in particular has been using them heavily, shrinking its supply and killing hundreds (if not more) in the process. Cluster Munitions Coalitions, a disarmament group devoted to monitoring the use of these weapons, estimated in August that cluster munitions had already killed almost 700 people in Ukraine.

“The researchers could not establish whether all of the nearly 700 people killed by the munitions were civilians, as the status of some had not been reported, but said that it was clear that the vast majority were not combatants,” The New York Times reported at the time.

The use of cluster munitions in any theater isn’t worth the price.

A Human Rights Watch report released Thursday found that in retaking the city of Izium from Russia last year, the Ukrainian military used cluster munitions to devastating effect. Those cluster munitions rocket attacks “killed at least eight civilians and wounded 15 more,” Human Rights Watch said, but the “total number of civilians killed and wounded in the cluster munition attacks that Human Rights Watch examined is most likely greater.” However, the Ukrainian defense minister denied in a letter to Human Right Watch that any cluster munitions were used around Izium last year, despite evidence Human Rights Watch had gathered and contemporaneous reporting from the Times.

That heavy toll on civilians is why cluster munitions are banned under international law. The U.S., notably, is not a signatory of the Convention on Cluster Munitions. Nor are Russia or Ukraine. But many members of NATO are, and some congressional Democrats support banning the export of the weapons altogether, which had the Biden administration reaching out last week to lay the groundwork among allies to try to smooth things over.

Admittedly, the situation in Ukraine is a little different from most. This isn’t a case like Yemen, where Saudi Arabia rained down U.S.-supplied cluster munitions for years. In Ukraine, the civilians who would be at risk are the very people the Ukrainians are trying to protect. Any cleanup campaign would fall on Kyiv to undertake once the war is over. But no matter what promises Ukraine makes about how these weapons will be used, the use of cluster munitions in any theater isn’t worth the price. This is a decision the Pentagon should rethink immediately, before even one of these weapons can be shipped off to the front lines.