BRUSSELS (Reuters) - World powers believe talks with Iran over its contentious nuclear program have been substantial enough for diplomacy to continue, a senior Western diplomat said on Monday, days after a meeting in Kazakhstan failed to yield a breakthrough.

"There is enough substance for these negotiations to continue," the diplomat told reporters. "I would not expect a breakdown."

The six powers - the United States, Russia, China, France, Britain and Germany - want Iran to scale back its nuclear program because of concerns it aims to give the Islamic Republic the capability of making an atom bomb. Iran denies that.

(Reporting by Justyna Pawlak; Editing by Adrian Croft)