US President George W. Bush said Wednesday that if Iran must not be allowed to develop nuclear weapons. On a surprise visit to Afghanistan, Bush said Iran should be allowed to have a civilian nuclear program, but that the "world is speaking with one voice" in opposing Iranian development of a nuclear weapon. "Iran must not have a nuclear weapon," Bush said during a news conference in the Afghan capital of Kabul. "The most destabilizing thing that can happen in this region and the world is for Iran to develop a nuclear weapon." In Moscow, the chief Iranian nuclear negotiator said Wednesday that there was no need for Tehran to resume a moratorium on uranium enrichment activity, Russian news agencies reported. "A moratorium is necessary when there is something dangerous. But all our activities are transparent," Ali Larijani said after arriving in Moscow for talks, according to the Interfax news agency. Larijani also said that Tehran agrees to all inspections by the International Atomic Energy Agency if they are conducted in line with international law, the RIA-Novosti news agency reported. Meanwhile, Russia's top diplomat reiterated Moscow's call for Iran to return to a moratorium on enriching uranium as a condition for taking part in a joint enrichment facility on Russian territory. "I do believe that a compromise that would not allow any violations of the nonproliferation agreement is possible," Russian Foreign Minister Sergey Lavrov told reporters in Budapest, where President Vladimir Putin is on a state visit. "What is necessary is for Iran to come back to the moratorium, to accept the joint venture proposal as a package that would be supported by the members of the governors' board of the IAEA. I'm not saying that this is already decided."