* Supreme leader backs president's push for negotiations
* Says talking does not mean compromising
* Talks with world powers resume in Geneva on Thursday
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 characterised 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.
"No one should consider our negotiators as compromisers," Khamenei said in a speech, a day before the Nov. 4 anniversary of the 1979 seizure of the U.S. Embassy in Tehran, a pivotal event in U.S.-Iranian relations, the ISNA news agency reported.
"They have a difficult mission and no one must weaken an official who is busy with work," said Khamenei, who wields ultimate power in Iran's dual clerical-republic system, including over the nuclear programme.
ENEMY WHO SMILES
Hardline factions, who oppose any thaw in relations with the United States, have criticised Rouhani's negotiating team for not releasing details of the proposal they made to world powers at a previous round of talks in Geneva last month.
They have also resisted calls from moderate Iranian newspapers and prominent figures including former President Akbar Hashemi Rafsanjani to drop the "Death to America" chant, often heard at Friday prayers throughout Iran.
Khamenei reiterated previous statements that he is not optimistic about the outcome of nuclear talks but said he saw no downside to holding the negotiations.
"With God's permission, we will not be harmed by these negotiations ... if the negotiations reach a conclusion then all the better, but if they don't it will mean that the country must stand on its own feet," Khamenei said.
He also criticised the United States for continuing to impose sanctions and threatening possible military action. Both Washington and its ally Israel say the military option to prevent Iran getting nuclear weapons is something they do not rule out.
"We should not trust an enemy who smiles," Khamenei said. "From one side the Americans smile and express a desire to negotiate, and from another side they immediately say all options are on the table."
In September, U.S. President Barack Obama insisted that the United States would "take no options off the table, including military options, in terms of making sure that we do not have nuclear weapons in Iran."