Russia Wednesday called on Iran to heighten cooperation with the UN atomic watchdog, but also criticized the United States and European Union for imposing extra nuclear sanctions outside the United Nations.

"Iran must ensure the required level of transparency and cooperation with the IAEA," Russia's UN ambassador, Vitaly Churkin, told the UN General Assembly.

"Clarification of outstanding questions regarding the Iranian nuclear programme would meet not only the goals of strengthening the non-proliferation regime but quite obviously the interests of Iran as well," he added.

Churkin added that "Russia sees no reasonable alternative to a political and diplomatic settlement of the Iranian nuclear problem."

The UN Security Council has imposed four rounds of sanctions against Iran over its refusal to stop enriching uranium, in parallel to talks between the Tehran government and Britain, China, France, Germany, Russia and the United States.

Churkin said though that sanctions were only to send "a strong signal" to Iran that it must cooperate and he denounced extra sanctions imposed by the United States, European Union and Japan.

"We strongly reject a situation when, parallel to the collective efforts in the UN Security Council, unilateral decisions on sanctions are made, including ex-territorial ones, which undermine the very foundation of further joint efforts.

"We must put an end to this practice that runs counter to international law and is negatively politically charged," Churkin said.