The U.S. Is Expected to Provide Cluster Munitions to Ukraine. Here Is Why They Are Controversial.

The United States appears to be on the verge of providing Ukraine with cluster munitions, a senior Biden administration official said. Kyiv has been pushing for the controversial and widely banned type of weapon but Washington has resisted because of its potential to cause indiscriminate harm to civilians.

Ukraine has said the weapons would help in its counteroffensive against Russian troops by allowing its forces to effectively target entrenched Russian positions and to overcome its disadvantage in manpower and artillery.

After months of demurring, citing concerns about the weapons’ use and saying they were not necessary, U.S. officials have recently signaled a shift. Laura Cooper, the deputy assistant secretary of defense for Russia, Ukraine and Eurasia, told U.S. lawmakers late last month that the Pentagon had determined that cluster munitions would be useful for Ukraine, “especially against dug-in Russian positions on the battlefield.”

The expected U.S. decision was first reported by National Public Radio and confirmed on Wednesday night by the administration official, speaking on condition of anonymity in order to disclose internal policy discussions.

Here is what to know about the weapons.

What are cluster munitions?

Cluster munitions, first used during World War II, are a class of weapons including rockets, bombs, missiles and artillery projectiles that break apart midair and scatter smaller munitions over a large area.

Why are they controversial?

Cluster munitions’ bomblets are generally designed to explode or ignite upon hitting the ground, but historically their failure rate is the highest among all classes of weapons, with lasting and often devastating consequences for civilians. According to humanitarian groups, a fifth or more of bomblets can linger, potentially to detonate when disturbed or handled years later.

“There’s just not a responsible way to use cluster munitions,” said Brian Castner, the weapons expert on Amnesty International’s Crisis Response Team.

Since World War II, cluster munitions have killed an estimated 56,500 to 86,500 civilians. They have also killed and wounded scores of American service members. Civilians, including children in Syria, Yemen, Afghanistan, Lebanon, the Balkans and Laos, continue to suffer from incidents involving remnants of cluster munitions.

What is the U.S. planning to send?

Under the decision, the United States would send Ukraine 155-millimeter artillery shells loaded with explosive grenades called dual-purpose improved conventional munitions, or D.P.I.C.M.s. The shells are designed to break open midair and dispense the grenades over an are to attack both armored vehicles as well as dismounted troops.

The two main 155-millimeter D.P.I.C.M. shells in the U.S. inventory are the M483, which contains 88 grenades, and the longer-range M864 which carries 72 grenades. Which version being considered for Kyiv is unclear.

Both shells use the same kinds of D.P.I.C.M. grenades, which often fail to immediately explode due to environmental factors, such as landing in vegetation or on soft ground. The grenades lack the ability to self-destruct, and often remain hazardous for decades afterward, capable of exploding if mishandled due to their particularly sensitive fuses, Mr. Castner added.

“If you touch that thing wrong,” he said, “it’s like striking a match.”

Aren’t these things banned?

Since cluster munitions spread over a large area and often explode long after they are deployed, they can indiscriminately harm civilians, which Mr. Castner said was a violation of international humanitarian law and a potential war crime.

Because of those risks, more than 100 countries — though not the United States, Russia or Ukraine — have signed a 2008 treaty known as the Convention on Cluster Munitions, promising not to make, use, transfer or stockpile them. Since the adoption of the convention, 99 percent of global stockpiles have been destroyed, according to the Cluster Munition Coalition.

Ukraine has said it would deploy the weapons judiciously, given that it is fighting on its own land, and that many frontline areas are already widely affected by land mines.

Have cluster munitions been used in Ukraine?

The New York Times has documented Russia’s extensive use of cluster munitions in Ukraine since the beginning of the invasion in February 2022. Ukraine has also used them in efforts to retake Russian-occupied territories, according to human rights monitors, the United Nations, and reports from The Times. The Cluster Munition Coalition said in its annual report last summer that cluster munitions had killed at least 689 people in just the first six months of fighting.

While the exact number of the weapons used in the conflict is difficult to know, hundreds have been documented and reported in Ukraine, mostly in populated areas, the group Human Rights Watch said in a May 2023 report. The attack with the highest known casualties was an April 2022 strike with a missile equipped with a cluster munition at a crowded train station in Kramatorsk, which killed dozens and injured more than 100 others, according to the group.

“Transferring cluster munitions disregards the substantial danger they pose to civilians and undermines the global effort to ban them,” Mary Wareham, the group’s arms advocacy director, said in a statement on Thursday.

How do other allies feel about these weapons going to Ukraine?

Most members of NATO, the Western military alliance that has been staunch in its support for Ukraine, have signed on to the international ban. Ms. Cooper, the deputy assistant secretary of defense, said “concerns about allied unity” were one of the reasons holding the United States back from providing the weapons to Ukraine. The Convention on Cluster Munitions also limits the ability of nations that have signed on to cooperate militarily with countries that employ them.

How would supplying cluster munitions affect the war?

Ahead of Ukraine’s long-anticipated counteroffensive, Russian troops have had months to prepare lines of defense against the coming assault, with miles of trenches, tank traps and mines. Ukraine and the Biden administration have argued that the cluster munitions could help the Ukrainian forces, which are outnumbered by the Russian military, overcome those defenses.

But this imprecise nature may also put offensive Ukrainian forces at risk of encountering unexploded munitions from earlier deployments, said a research associate at the Arms Control Association, Gabriela Rosa Hernández.

In February, Oleksandr Kubrakov, Ukraine’s deputy prime minister for restoration, said speedy provision of arms from allies would be critical to Kyiv’s advance in the counteroffensive against Russia, and that it should be Ukraine’s choice to deploy the weapons on its soil.

“It’s our territory. I understand how it’s complicated with all these conventions,” he said in a town hall at the Munich Security Conference, but he stressed their usefulness in resisting the Russian invasion. “Our allies, the U.S., many other countries, they have millions of rounds of such type. Again, we will wait, wait, wait, and suddenly one day, probably, we will receive such type of munitions.”

Eric Schmitt, John Ismay and Gaya Gupta contributed reporting.