Almaty (Kazakhstan), Feb 28 (IANS/RIA Novosti): Talks between Iran and six world powers being conducted over the former's disputed nuclear programme concluded here Wednesday without reaching any agreement. But the two sides pledged to hold further meetings in the coming weeks.

The six world powers -- Britain, China, France, Germany, Russia and the US -- 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 believe Iran is attempting to build an atomic weapon. Tehran insists its programme has entirely peaceful objective and decried international pressure as unacceptable interference in its sovereign affairs.

Iran's chief negotiator Saeed Jalili said Wednesday the talks had seen a modicum of progress, and proposals by the world powers were "closer to Iran's position".

"Their proposals seem more realistic and positive," he said.

And despite the lack of a breakthrough at the first talks between the sides since last June's meeting in Moscow, Russia's chief negotiator at the two-day talks, Deputy Foreign Minister Sergei Ryabkov, described the negotiations as "extremely useful".

"A number of aspects to the resolution of the issue and means of increasing trust were considered," he said, without elaborating.

The two sides agreed to meet again at expert level in Istanbul March 17-18 and to hold high-level talks in Kazakhstan April 5-6.

New US Secretary of State, John Kerry, said Monday the opportunity for negotiations could not "remain open forever".

International sanctions against Iran have hit the Islamic republic's economy hard, and seen the near collapse of its national currency, the rial.