Iran will not accept a weak uranium enrichment programme which world powers might be willing to grant the Islamic republic like a "toy" in nuclear negotiations, a top official said Sunday.

The size and scale of the Islamic republic's enrichment activities remain the biggest stumbling block in efforts to clinch a long-term agreement over Iran's disputed atomic activities.

Majid Takht-Ravanchi, Iran's deputy foreign minister for American and European Affairs, made the remarks on returning to Tehran from Geneva, after five hours of talks with US officials.

"We said to the other party ... we will not accept that our uranium enrichment programme becomes something like a toy," he said, referring to last week's discussions.

"Our enrichment programme has a specific framework and we cannot accept anything outside of this framework," he added.

Iran and six world powers failed to clinch a comprehensive agreement by a July 20 deadline, which has now been extended to November 24.

The next round of nuclear talks will be held before the UN General Assembly, which starts on September 16.

The five permanent members of the UN Security Council -- Britain, China, France, Russia and the US -- plus Germany, want to render Iran incapable of developing an atomic weapons capability.

In exchange, Iran wants an end to extensive sanctions that are choking its economy as well as sufficient enrichment capacity to guarantee fuel for its sole nuclear power plant in Bushehr after a current supply contract with Russia expires in 2021.

The process of enriching uranium can produce fuel for reactors but also the core of a nuclear bomb if purified to higher levels.

Iran has always denied that it is pursuing an atomic bomb.