Iran has given an assurance that it would stop enriching uranium to 20 percent purity if world powers agreed to a proposed nuclear fuel swap, Turkish Foreign Minister Ahmet Davutoglu told reporters in Istanbul.

The offer, conveyed to Davutoglu on July 22, could bode well for an expected resumption of talks in September between Iran and major powers on the Islamic Republic's atomic programme, which Tehran says is for peaceful purposes and not for bombs.

Asked about Davutoglu's comments, the US State Department said Iran had often sent mixed signals but that the United States was "fully prepared" to resume talks among the six major powers and Tehran about Iran's nuclear programme.

Iran last met the United States, Britain, China, France, Germany and Russia in Geneva in October, when they discussed Iran sending some low-enriched uranium abroad in exchange for fuel for a Tehran reactor that makes medical isotopes.

Uranium enrichment is a process that can produce fuel for nuclear reactors or, if carried out to a much higher degree, can yield fissile material for atomic bombs.