By Yeganeh Torbati DUBAI (Reuters) - Iran's supreme leader gave strong backing on Sunday to his president's push for nuclear negotiations, warning hardliners not to accuse Hassan Rouhani of compromising with the old enemy America. Ayatollah Ali Khamenei's comments will help shield Rouhani, who has sought to thaw relations with the West since his surprise election in June, from accusations of being soft on the United States, often characterized in the Islamic Republic as the "Great Satan". Iran will resume negotiations with six world powers, including the United States, in Geneva on Thursday, talks aimed at ending a standoff over its nuclear work that Tehran denies is weapons-related. Rouhani hopes a deal there will mean an end to sanctions that have cut the OPEC country's oil exports and hurt the wider economy, but any concession that looks like Iran is compromising on what it sees as its sovereign right to peaceful nuclear technology will be strongly resisted by conservatives.