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Rights groups have called on to stop using cluster munitions in , saying fatal strikes using the indiscriminate weapons on a hospital and a school could constitute war crimes.

said cluster bombs hit a preschool in northeastern Ukraine on Friday that was being used to shelter civilians, killing three people, including a child.

The rights groups said the attack in the town of Okhtyrka "may constitute a war crime", after images showed cluster munitions struck at least seven locations on or near the school.

Amnesty said the attack "appears to have been carried out by Russian forces, which were operating nearby, and which have a record of using cluster munitions in populated areas".

"There is no possible justification for dropping cluster munitions in populated areas, let alone near a school," Amnesty Secretary General Agnes Callamard said in a statement on Sunday.

Over 100 countries have signed the 2008 Convention on Cluster Munitions banning the production and use of the weapons, but not Russia or Ukraine.

Missiles carrying explode in the air and send dozens or hundreds of small bomblets over a large area.

They often fail to explode on impact, thus becoming landmines to anyone who comes across them.

Human Rights Watch said on Friday that Russian cluster munitions had hit a hospital in Vuhledar in eastern Ukraine, killing four civilians and injuring 10, six of them healthcare workers.

"This callous attack has killed and injured civilians, and damaged a hospital," said HRW's arms director Stephen Goose.

Launching indiscriminate attacks that kill or injure civilians constitutes a war crime, and hospitals and school are afforded further special protection under international law.

Investigative website Bellingcat has been collating reports of cluster bomb use in Ukraine and said that second city Kharkiv "also appears to have been the target of multiple cluster munition attacks".

"Images and videos posted online demonstrate even wider use of these weapons in civilian areas," Bellingcat said, reproducing dashcam footage of a driver trying to avoid a hail of bomblets in Kharkiv.

"This stretch of highway runs through a residential area and is immediately next to a children's hospital," Bellingcat said.

The International Campaign to Ban Landmines and Cluster Munition Coalition (ICBL-CMC) "strongly condemned" their use in Russia's invasion of Ukraine and called for "an immediate end to their use".

"Cluster munitions are indiscriminate weapons that overwhelmingly kill and injure civilians, and leave a deadly legacy of contamination threatening lives and hindering recovery for years to come," the ICBL-CMC said.