Germany's Chancellor Angela Merkel criticized Russia's decision to lift an arms export ban on Iran, asking countries to remove sanctions together.

Merkel "pleaded for sanctions against Iran to be removed as cohesively as possible," but insisted there was "no reason" why nuclear talks with Iran could not go on as they had until now.

Tehran signed a framework nuclear deal on April 2 after lengthy discussions with the 5+1 group, including the five permanent members of the UN Security Council - Russia, China, US, France and Britain, and Germany.

Under the agreement, Iran would agree to restrict its nuclear activities to producing energy for civil purposes in return for a relief from sanctions. The German chancellor said on Tuesday it was imperative that Iran fulfil all conditions before sanctions were removed.

However, Russian President Vladimir Putin signed a decree on Monday, removing a ban to supply S-300 missiles to Iran. A day later, Moscow announced that it could deliver the missile systems as early as this year, angering Western countries who were part of the combined nuclear talks with Tehran.

Nuclear talks between Iran and world powere were to resume on April 21, said Iran's Foreign Minister Mohammad Javad Zarif during a trip to Madrid.

"My colleagues, with the deputy to [European Union foreign affairs chief] Federica Mogherini and other political directors...will get together next Tuesday to start drafting," Zarif said, adding that his country would implement "irreversible steps" on nuclear program if the West matches it.

The final deal is due to be signed on June 30.

mg/jr (AFP, Reuters, AP, dpa)