Surgeons in the rebel hub of Donetsk in eastern Ukraine, where dozens of civilians have died in recent weeks, confirmed on Tuesday that some patients were victims of cluster bombs, as alleged by Human Rights Watch. Although Kiev vehemently denied that its troops battling the pro-Russian insurgency in the east were using the controversial and indiscriminate cluster munitions, medics claimed Ukrainian forces were at fault. "I have removed fragments of sub-munition weapons used by Ukrainians from the injured dozens of times," said a surgeon in Donetsk's Kalinin hospital, one of the facilities treating wounded civilians. Human Rights Watch (HRW) published a report identifying 12 incidents in which the highly imprecise munitions killed six people, including a Swiss aid worker, earlier this month. Cluster bombs are munitions that contain dozens or even hundreds of explosives carried by bombs or rockets and "spread indiscriminantly over a wide area, often the size of a football field", Human Rights Watch noted. "These arms are not for destroying buildings; they are uniquely for killing people," the surgeon working in the Kalinin hospital said. "The little darts cause grave injuries. There have been cases when we found up to 20 or 30 of them in one person." Most of the world has signed a treaty banning cluster bombs, but not Ukraine, and nor have the United States and Russia. Kiev, however, has denied using the weapons, blaming the separatists and vowing to launch a full investigation into the reports. "These charges are groundless," said Ukrainian defence spokesman Bogdan Senyk. Several kilometres from the Kalinin hospital, a pro-Russian rebel leader at a checkpoint showed unexploded shells filled with sharp 2cm-long fragments. He said that Ukrainian forces had pounded the city from outlying positions with cluster munitions "since the beginning of the war", launching them with Grad and Uragan truck-mounted weapons systems. "I have operated on a patient who was injured by one of these darts," a surgeon at hospital No 17, who introduced himself as Nikolai, said.