Both Russian and Ukrainian forces have used cluster munitions that have killed Ukrainian civilians, Human Rights Watch said in a report on Thursday as the U.S. weighs whether to answer the Ukraine government’s call to supply it with the weapons.

Human Rights Watch, an international advocacy group, called on both Russia and Ukraine to stop using the weapons, and urged the U.S. not to supply them.

More than 120 countries have signed on to an international treaty banning the weapons, which typically scatter a large number of smaller so-called bomblets over a large area that can kill or maim unwary civilians months or years later.

Russia, Ukraine and the U.S. have all to declined to sign the treaty.

A senior Pentagon official said late last month that cluster munitions would be useful for Ukraine in pushing back against Russian forces, but they had not been approved for Kyiv yet because of congressional restrictions and concerns from allies.

Ukraine fired cluster munition rockets into Russian-controlled areas in and around the eastern Ukrainian city of Izium last year after Russia invaded Ukraine, Human Rights Watch said, citing interviews with more than 100 residents, witnesses and local emergency personnel.

The Ukrainian attacks killed at least eight civilians and wounded at least 15 civilians in Izium, Human Rights Watch said.

The group has previously reported that Russia’s use of cluster munitions in Ukraine has killed scores of civilians, and the United Nations’ Human Rights Council has also documented the use of such bombs by both sides.

“Cluster munitions used by Russia and Ukraine are killing civilians now and will continue to do so for many years,” Mary Wareham, the group’s acting arms director, said in a statement. “Both sides should immediately stop using them and not try to get more of these indiscriminate weapons.”

The Ukraine government has urged members of the U.S. Congress to press President Joe Biden’s administration to approve sending over cluster bombs.

What are cluster bombs?

A cluster bomb is a type of munition that breaks apart into smaller parts which spread their damage over a wider area. They can be firsd through planes, missiles and artillery.

The smaller parts of the bomb are built so they explode on impact. However, sometimes the bomblets become a ‘dud’ which means they will just fall on the ground without exploding.

In the latter case, the bomb becomes a sort of landmine. Although they did not work as originally intended, they are still active and can damage vehicles or people that come into contact with tem even after years.

The Convention on Cluster Munitions has been signed by 120 countries which prohibit making and using the weapons. Human rights groups say that cluster bombs lead to indiscriminate killings. According to Reuters almost 60% of those killed through cluster bombs are civilians underatking daily activites.