Much of the world says they're immoral. So why is Ukraine so keen on cluster bombs?

Cluster munitions are responsible for the deaths of thousands of civilians and have been banned in more than 120 countries, but military experts say they would be an effective weapon for Ukraine's army against Russian forces, which is why the United States has decided to provide them.

"There's no question these things are very effective," said Mark Cancian, a senior adviser with the International Security Program at the Center for Strategic and International Studies in Washington, D.C.

"It will be a useful increase in artillery effectiveness," he said. "It's not going to be a game changer, but in the end, it will make Ukraine virtually more effective."

Ryan Brobst, a senior research analyst with the Center on Military and Political Power at the Foundation for Defence of Democracies in Washington, agreed. But, he said, "what would be a game changer is if Ukraine completely ran out of artillery, ammunition."

"[This] allows several hundred thousand more artillery rounds to be available to them," he said.

The decision by the U.S. last week to provide cluster munitions has been condemned by human rights groups, along with some NATO countries who signed the 2010 convention banning their use, production or stockpiling. The U.S. has not signed the convention.

A cluster munition is a bomb that opens in the air and releases smaller "bomblets" across a wide area. The bomblets are designed to take out tanks and equipment, as well as troops, hitting multiple targets at the same time.

Michael Kofman, director of the Russia Studies Program at the Virginia-based Center for Naval Analyses, suggested in a series of Twitter posts that such weapons "could have a significant impact" for Ukraine's counteroffensive and that despite the drawbacks, "unlocking this stockpile has important implications for the course of Ukraine's offensive."

"Without this ammunition, it is difficult to imagine this offensive taking place, he wrote.

Ukraine is in need of ammunition. The U.S. has been supplying, from its own stocks, traditional 155-mm howitzer munitions and has sent more than two million rounds to Ukraine. Allies across the globe have provided hundreds of thousands more since Russia invaded its neighbour on Feb. 24, 2022.

But, as noted by Cancian, the inventory of standard, high-explosive artillery shells is now very low.

"Although the United States continues to provide some shells as new production becomes available, the numbers are not sufficient to meet Ukraine's artillery needs. Cluster munitions will fill that gap," he recently wrote.

Ukraine's counteroffensive against Russian troops is not going as rapidly as had been hoped, Cancian said. "They need a boost ... and the United States has basically run out of regular artillery. This is what's available."

Ukraine wants cluster munitions because they are highly effective against area targets, such as infantry, artillery and vehicle convoys, he said.