GENEVA (Reuters) - The number of people killed or wounded by cluster munitions increased eightfold last year to more than 1,000, mostly due to their use in the Ukraine war, particularly by Russia, a campaign group said on Tuesday.

Cluster bombs, banned by more than 100 countries, are fired from the ground or by aircraft and explode mid-air, spraying smaller 'bomblets' over a wide area.

Survivors often suffer severe injuries from blasts and burns that can result in life-long medical needs, and campaigners worry in particular about unexploded bombs that remain on the battlefield long after a conflict ends.

Of the 1,172 victims last year, 353 died, the report by the Cluster Munitions Coalition campaign group showed. That is the highest level since the group began compiling its annual reports 14 years ago.

The report said that nearly all the victims were civilians and three-quarters were children who are often drawn to play with unexploded bomblets.

In Ukraine, it said Russia had used cluster munitions "repeatedly", while Ukraine had also used them, but to "a lesser extent". It did not provide a breakdown.

The report covered last year, and excludes this year's use by Ukraine of cluster munitions from the United States, which Kyiv began receiving in July.

Kyiv says it is using them only against Russian troops at the frontline. Russia has denied using them at all but has threatened to do so in response.

Unlike in past years where casualties have nearly always been caused by the delayed explosion of bomb remnants, most of the 2022 casualties were from live bombs, the report said.

Both Moscow and Kyiv deny targeting civilians in the war that began with Russia's invasion in February 2022, during which Russian forces have razed several Ukrainian cities to the ground.

Neither country is party to a 2008 convention that prohibits the use of cluster munitions, nor is the United States.

In deciding to send them to Ukraine this year, Washington said the weapons have legitimate uses on the battlefield against military targets, and would save lives if they hastened the end of the war. It also said its cluster munitions leave behind far fewer unexploded bomblets than those used by Russia.

The report documented the first known use of cluster munitions in Myanmar last year, as well as use in Azerbaijan, Iraq, Laos, Lebanon, Syria and Yemen.

(Reporting by Emma Farge; Editing by Peter Graff)