Talks between Iran and six world powers on the Islamic Republic’s disputed nuclear program ended in Almaty, Kazakhstan without agreement on Wednesday, but the two sides pledged to hold further meetings in the coming weeks.

The six world powers - Britain, China, France, Germany, Russia and the United States - had proposed scaling back sanctions against Iran in exchange for the closure of its underground Fordo enrichment facility and an undertaking to halt the enrichment of uranium to 20 percent.

A level of enrichment greater than 20 percent is the very minimum needed to make a crude nuclear device, scientists say, although most nuclear bombs use the heavy metal enriched to 90 percent.

Western powers say Iran is attempting to build an atomic weapon, but Tehran insists its program has entirely peaceful purposes and has decried international pressure as unacceptable interference in its sovereign affairs.