Tehran: Iran has resumed small-scale enrichment of uranium, a senior Iranian nuclear negotiator says - a defiant declaration in the face of global opposition to Iran's atomic programme.

Javad Vaeidi, deputy secretary of Iran's Supreme National Security Council, said enrichment of uranium resumed last week at Natanz, the country's main enrichment plant, but that Iran had not resumed large-scale enrichment, as required for producing fuel for nuclear reactors.

Later Tuesday, Vice President Gholamreza Aghazadeh said resumption of uranium enrichment work was very limited.

"It can't be used even at semi-industrial level. It's only at the laboratory stage for analyzing research activities. This sort of enrichment cannot be used (for producing nuclear fuel)," he said.

Gholamreza Aghazadeh, director of Iran's atomic programme, was quoted by the ISNA student news agency as saying the centrifuge work relaunched at the Natanz pilot fuel enrichment plant was on a "small and laboratory scale".

The resumption still leaves Iran a long way from reaching the stage the world fears most: large-scale enrichment of uranium - a process that can produce fuel for an atomic bomb.

Vaeidi also told reporters that Iran would resume negotiations with Moscow on February 20 over its plan to enrich Iranian uranium on Russian soil - a proposal designed to allay fears that Iran will build nuclear weapons.

"The talks with Russia remain valid," Vaeidi said, adding that an Iranian delegation would go to Moscow.

The negotiations with Russia had been due to resume on Thursday, but Iran said Monday they were postponed indefinitely.

In caracas, Venezuela, Iranian parliament speaker Gholam Ali Haddad Adel denied his country had flouted international rules by resuming small-scale uranium enrichment activities at Natanz, the country's main enrichment plant.

"All we've done is reinitiate nuclear energy research at the laboratory level," said Haddad Adel. "We have not said anything new or committed any crime."

Later in a speech to Venezuela's National Assembly, Haddad Adel denounced the U.S. and other nuclear powers for possessing "thousands of nuclear warheads ... (used for) threatening other non-nuclear countries."

"Mutual help is necessary in these circumstances," he said. "Iran and the Mideast and Venezuela and Latin America can act as two convergent axes to neutralise the plans of arrogant world (powers)."

Iran insists that as a signatory to the Nuclear Nonproliferation Treaty, which provides for peaceful nuclear development, it is entitled to enrich uranium for nuclear reactors. It has threatened to withdraw from the treaty if it was not allowed to exercise that right.

Vaeidi nonetheless indicated Iran was still open to negotiation.

"We are still prepared to find a formula to clarify the ambiguity in talks with our partners. At the same time, we will pursue our rights," he said.

Mohammad Saeedi, deputy head of the Atomic Energy Organisation of Iran, said on Tuesday that Iran has stopped allowing short notice inspections of its facilities by International Atomic Energy Agency (IAEA) inspectors.

He said on state television that some IAEA cameras need to be removed from Iranian nuclear facilities and that Iran was "taking the preparatory measures to do that."

The world has long sought to stop Iran from enriching uranium, fearing that the process would bring it to the threshold of possessing nuclear bombs.

On February 4, the IAEA reported Iran to the UN Security Council and called on its government to suspend all enrichment-related activities.

Instead, Iran suspended certain aspects of its co-operation with the IAEA.