World powers gave no ground to Iran at negotiations in Almaty last month and only recognised some of Tehran's rights, the Islamic republic's supreme leader said on Thursday.
"At the (February 26-27) meeting, the Westerners did nothing of importance that could be termed a gesture," Ayatollah Ali Khamenei said in speech reported on his website.
"All they did was recognise a part of the rights of Iran" to develop nuclear energy, he said, adding that the next meeting, due to take place on April 5-6 in the Kazakh city, would "help gauge the sincerity" of world powers.
Khamenei also condemned the international sanctions slapped on Iran over its controversial nuclear programme as a ploy "to push the people to oppose the Islamic regime."
Iran held talks with the five UN Security Council permanent members -- the United States, China, Russia, Britain and France -- plus Germany on its nuclear ambitions.
The meeting saw the group offer Iran a softening of non-oil or financial sector-related sanctions in exchange for concessions over the country's uranium enrichment operations.
"Some of the points raised in their (the world powers') response were more realistic, compared to what they said in the past," chief Iranian negotiator Saeed Jalili said at the time.
President Mahmoud Ahmadinejad later added that "negotiations are better than confrontation," while Foreign Minister Ali Akbar Salehi said "things are taking a turning point."
Western powers suspect Iran's nuclear programme to be a cover for building an atomic weapons capability, a charge which Tehran strongly denies.