By Marcus George
DUBAI (Reuters) - Iran's nuclear negotiators returned home as heroes on Sunday, greeted by jubilant supporters after securing a deal with world powers over the country's disputed atomic program.
Two days on, Iran's political realities are sinking in.
To ensure the deal stays on track, Iran's new moderate government needs to protect it from virulently anti-Western security hardliners who wield great economic and political power and are close to Supreme Leader Ayatollah Ali Khamenei.
Those voices are mostly silent as yet, but as the complex accord's costs and benefits are weighed by Iran's factionalized political class, hardliners who call the United States and its allies "world arrogance" will be poised to pounce.
"Major opposition is limited at the moment, but whichever parties have benefited from the status quo of sanctions and a closed economy stand to lose," said Siavush Randjbar-Daemi, a lecturer on Iranian politics at the University of Manchester in Britain.
"The agreement is still frail and the sense of urgency for talks on the next stages shows that things are on thin ice and the Iranian side needs to continue the momentum."
President Hassan Rouhani and Foreign Minister Mohammad Javad Zarif are increasingly popular: Iranians sense that the deal may solve the nuclear stand-off and end sanctions that have done serious damage to Iran's economy.
But they must contend with critics such as the ultra-conservative Kayhan newspaper, which has questioned the divergence of views between Iran and the United States over a key part of the text: Iran says its right to enrich uranium has been recognized, while U.S. officials maintain that is not the case.
"The fact that American leaders undermined the deal several hours after (they signed it) - before the ink was even dry - shows that the root of the challenge of dealing with untrustworthy America remains," Kayhan said in an editorial.
Such interpretations could gain traction among Iranians, especially if hawks in the U.S. Congress at the same time succeed in blocking further attempts at rapprochement.
"If the U.S. backs away from the deal or it's undercut by Congress, that feeds the hardliners in Iran," said Scott Lucas of EA Worldview, a news website that monitors Iranian media.
The situation leaves Khamenei - who quickly endorsed the achievement - in a bind.
He now faces the challenge of weighing the vision of the government against that of hardliners to whom he owes a lot, not least snuffing out the threat to his authority from millions of protesters who disputed the 2009 presidential election.
"The supreme leader will have a difficult balancing act to maintain. He will have to apply the best of his skills to keep the moderates and the conservatives happy," said Iranian-born Meir Javedanfar, a lecturer on Iranian politics at the Interdisciplinary Centre at Herzliya, Israel.
"On one hand he needs Rouhani ... to reach a deal with the West. On the other Khamenei also needs the support of the conservatives as they have been his most loyal allies."
While Iran says its nuclear program is peaceful, the West suspects it is aimed at developing nuclear weapons.
Since the agreement was sealed, Rouhani's government has gone on a charm offensive in an attempt to shore up support from conservative groups and their constituencies.
Within hours Rouhani gave a news conference alongside the families of Iranian nuclear scientists who were assassinated in Tehran in attacks Iran blamed on Israel.
"It's a shame your father (martyred nuclear scientist) isn't here with us today; be assured his memory lives on," Rouhani's office quoted him as saying. It sent a Twitter message with a picture of the president kissing the head of a young girl.
Since returning home, Zarif has also polished his own revolutionary credentials. On Monday, he honored the sacrifice of those killed in the Iran-Iraq war, a central pillar of the uncompromising views on national security held by hardliners, and also met the families of killed nuclear scientists.
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"This was a pre-emptive move, a very astute political move," said Mehran Kamrava, of Georgetown University in Qatar. "He was extremely sympathetic to their loss ... so it would not appear the loss was in vain."
Zarif has also emphasized the threat the agreement is under from Iran's enemies abroad, namely Israel, in what appears to be another way to get Iran's conservative critics on side with the deal. His message appears to be: 'if Netanyahu doesn't like it, that's good news'.
The government has been sure to invoke Khamenei's endorsement of the agreement.
But that was not as resounding as they made out.
In reply to a letter of congratulation from Rouhani thanking him for his support, the supreme leader appeared to pay homage to the uncompromising anti-Western resistance of Iranian officials over the last eight years.
His message read, in part: "God willing, persistence against those who want too much should always be the criteria for ... officials."
"IRAN IS YOUR BROTHER"
Mehran Kamrava commented that Khamenei had given himself some political "elbow room" in case the deal collapsed.
"Historically the supreme leader is supposed to be above the fray. So if the deal goes south, he won't have put himself out," Kamrava said.
Not wanting to be seen as the cause of the agreement's failures, Iranian hawks have instead busied themselves with firing broadsides at the West rather than at the accord itself.
"America and the arrogant enemies of the Islamic revolution talk of military options against the Islamic Republic. This is no more than bluff and exaggeration," the commander in chief of the Revolutionary Guards, Mohammad Jafari, said on Tuesday.
"The smallest military mistake that is made with regard to Iran and Americans would see the most historic loss, and many U.S. facilities and those of their allies in the region and outside would be in the cross-hairs."
Parliament speaker Ali Larijani, credited with spoiling a nuclear deal brokered by former President Mahmoud Ahmadinejad with world powers in 2009, also lashed out over statements by Western powers that they had acted to protect the region.
"You have set fire to the east and west of the Middle East and then you speak of security in the region. Afghanistan, Pakistan, Iraq and Syria are ablaze because of you," he said.
"We say to leaders of regional countries, don't be under the influence of the intrigues of the American government or the Zionist usurper. Iran is your brother. We are all followers of one prophet and one religion."
(Corrects to Iraq in penultimate paragraph)
(Additional reporting by Isabel Coles, Stephen Kalin and Jon Hemming; Editing by William Maclean and Giles Elgood)