Dieters were given fresh hope Sunday after scientists said they had developed a technique that could make weight loss permanent by using ultrasound to zap fat cells.

Evidence for the high-intensity focused ultrasound [HIFU], used with another treatment that involves freezing fat cells, has been identified in studies as having the potential to achieve weight loss without surgery.

Mark Whiteley, a senior vascular surgeon from Guildford, southeast England, told a meeting of the Royal Society of Medicine that the technique would be effective for destroying small areas of stubborn fat.

 "Our results have been very good and, from the previously published studies, it appears that HIFU and cyolipolysis -- or fat freezing -- are the only two methods of non-surgical fat removal that show any promise," Whiteley said. "Other techniques using lasers of other types of ultrasound don't work because they only damage fat cells, rather than destroying them, so the cells simply grow back."

Until now, the only permanent way of removing fat has been liposuction, which involves fat being surgically sucked out.

But Stephen O'Rahilly, professor of clinical biochemistry at Cambridge University, warned that the treatment could have very damaging effects.

"As a cosmetic treatment this would be fine, but if you kill off the fat cells on someone's stomach and they start to regain weight, you would run the risk of the fat being stored in the heart or liver, where it could be very dangerous and cause real organ damage," he said.