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.”

“The worst thing for civilians in Ukraine is to lose the war,” Kahl said. “We want to make sure that the Ukrainians have sufficient artillery to keep them in the fight in the context of the current counteroffensive, and because things are going a little slower than some had hoped.”

Kahl argued the U.S.-provided munitions have a much lower dud or failure rate while the Pentagon was working with Ukraine to minimize damage to civilians from the munitions, including winning assurances from Kyiv to provide accurate assessments on where they are used. He said the munitions were a temporary “bridge” as defense production ramps up to produce more regular artillery shells.

At least 38 human rights organizations have publicly opposed the transfer of cluster munitions to Ukraine, where the weapons have already been used in the war to devastating effect.

“These are already all over the country and will need to be cleaned up. That is not a good enough excuse for the United States to be sending more,” said Sarah Yager, the Washington director at Human Rights Watch (HRW). “Legislators, policymakers and the Biden administration will probably think twice when the pictures start coming back of children who have been harmed by American-made cluster munitions.”

Kyiv has long requested the cluster munitions. Ukrainian officials have asked for nearly every advanced weapon system from western allies.

After the U.S. decision leaked, Ukrainian presidential office adviser Mykhailo Podolyak said “the number of weapons matters” in the “great bloody war” with Russia.

“So, weapons, more weapons, and more weapons, including cluster munitions,” Podolyak tweeted on Friday.

Eighteen members of the Western security alliance NATO have banned cluster munitions and are unlikely to approve of the decision to transfer them to Ukraine.

Germany’s Foreign Minister Annalena Baerbock said Friday that Berlin stands by a major treaty banning the use of the weapons, according to several news reports.

NATO Secretary-General Jens Stoltenberg declined to comment on the U.S. decision but said at a Friday news conference that individual members were free to make their own choices regarding the weapons.

Pentagon press secretary Brig. Gen. Pat Ryder said “unity continues to remain very strong” across the alliance during a Thursday briefing.

The cluster munitions headed to Ukraine include those for a 155 millimeter Howitzer artillery gun, part of a broader package for Kyiv announced Friday.

Concerns for accuracy

Congress passed a law in 2009 that says the U.S. cannot deploy or transfer cluster munitions with a dud rate higher than 1 percent. The president can sign a waiver to bypass that restriction. Existing laws also prohibit the use of the weapons in civilian areas.

Ryder on Thursday said they have “multiple variants” of cluster munitions and Washington would not deliver those with a rate higher than 2.35 percent. He said they would select the lowest rate possible. Kahl confirmed the same figure on Friday.

But human rights groups have said the Pentagon has not been transparent with the data on dud rates and are calling for more clarity. There is also concern about accuracy and that some bombs, including the 155 mm weapons, have a much higher failure rate than reported.

Both Russia and Ukraine have allegedly used cluster munitions in the war so far, which human rights organizations say has led to civilian deaths.

Russia’s dud rate is reportedly as high as 40 percent, while Ukraine’s is as high as 20 percent, according to Yager from HRW. Yager also said the bombs already deployed constitute a $73 billion cleanup effort.

The Pentagon maintains the cluster munitions could help Ukraine advance and stop the Russian bombings. But Eric Eikenberry, the government relations director at Win Without War, countered the argument as “speculative.” 

“We’ve already seen this in conflict,” Eikenberry said, dismissing “the idea that these are going to be a huge boon, the counteroffensive is going to jet forward and we’re going to save lives in the aggregate because these are going to be the wonder weapons that flip the battlefield in our favor and takes Russian artillery out of commission.”

Eikenberry said the U.S. was losing its moral high ground by providing the weapons, which he said has been key to maintaining a cohesive international coalition backing Ukraine.

“You’re starting to introduce chinks in the armor of the moral argument Ukrainians have in the situation,” he continued.

Cluster munitions have been used since World War II and have led to tens of thousands of civilian casualties, particularly in Laos, where the U.S. dropped millions of bombs in the ‘60s and ‘70s. Civilians in Laos still struggle to overcome unexploded ordnance. The U.S. last deployed cluster munitions in Iraq in 2003.

Along with Russia and Ukraine, the U.S. is not a party to a major 2008 treaty, the Convention on Cluster Munitions, signed by 123 countries. Signatories pledge not to use cluster munition weapons in war.

Republicans on the House and Senate Armed Services and Foreign Relations committees have supported cluster munitions for Ukraine. 

The chairs of each committee sent a letter earlier this year to Biden requesting the approval of the weapons, saying U.S. versions were “highly effective” and advanced enough to minimize damage against civilians.

Several Democrats have voiced opposition to the cluster munitions package.

Rep. Chrissy Houlahan (D-Pa.), co-chair of the bipartisan Unexploded Ordnance and Demining Caucus, said “victory cannot come at the expense of our American values and thus democracy itself.” 

“Cluster munitions are indiscriminate, and I strongly oppose providing these weapons to Ukraine,” she said in a statement. “There are some who will say that these weapons are necessary to level the battlefield given Russia’s reported use of them. 

“To those individuals, I challenge the notion that these weapons are the most effective support we can provide Ukraine right now,” the lawmaker added. “I challenge the notion that we should employ the same tactics Russia is using, blurring the lines of moral high ground.”