A powerful type of cluster munition rocket not previously seen in the Syrian conflict is possibly being used by regime forces, Human Rights Watch said in a statement on Wednesday.

Basing its statement on photos taken after a recent attack in the central city of Hama, HRW said the images suggested the government had deployed 300 mm 9M55K surface-to-surface rockets.

The weapon, which carries dozens of submunitions, is Russia, according to Agence France-Presse.