Supreme leader Ayatollah Ali Khamenei said on Tuesday that Iran will reject any dialogue if its outcome is pre-determined by Washington,raising the possibility a mooted nuclear fuel deal may be derailed. Khamenei's comments came as world powers turned up the heat on Iran to accept the UN-brokered nuclear deal,with US Secretary of State Hillary Clinton saying Iran was at a "pivotal moment" to show it did not want to be isolated from the international community. Iran is engaged in high-profile UN-hosted talks with world powers over how to procure nuclear fuel for a Tehran research reactor. But officials here are increasingly opposed to the proposed deal under which Iran would send low-enriched uranium (LEU) abroad for conversion into fuel for the Tehran reactor. They say they would rather buy the fuel directly. Today,Khamenei,Iran's all-powerful leader who has the final say in all national issues,raised the possibility the UN-brokered deal may fail. "We do not want any negotiation,the result of which is pre-determined by the United States," Khamenei said in a speech on the eve of Wednesday's 30th anniversary of the US embassy seizure by radical students.