The first thing Rouhani did on his return to Tehran at the weekend was to state that he had acted within guidelines set by Supreme Leader Ayatollah Ali Khamenei when he took part in the highest-level contact between Iran and the United States in three decades.

The brief mobile phone conversation led many to speculate that since the election of the moderate Rouhani relations between Washington and Tehran, in the deep freeze since the US embassy hostage crisis, may be about to improve.

Rouhani's invocation of Khamenei, the man at the top of Iran's complex political system, looked like a bid to ward off a backlash from hardline power centres and their supporters, some of whom were already lying in wait to throw eggs at the President's motorcade.

The demonstrators' chants of "Death to America" were, however, likely to be only the opening shots of a campaign against Rouhani by a conservative political and military establishment opposed to the West in general and to the United States and Israel in particular.

Such is the mistrust between Iran and the United States that a big sticking point of negotiations over Tehran's disputed nuclear programme has been who should make the first move.

Iran has insisted the United States and the European Union should ease sanctions before it makes any concessions over enriching uranium, while Western powers have argued the reverse.

For Iranian hardliners, Rouhani's conversation with Obama was a step too far and, they argue, Washington must now take concrete steps to dispel the distrust.

"The Americans should prove their goodwill by taking practical steps (such as) ending enmity with the Iranian nation and lifting sanctions," a senior member of Parliament's National Security and Foreign Policy Commission, Hossein Naqavi Hosseini, said on the assembly's website on Sunday.

The head of Iran's elite Revolutionary Guards, which are backed up by a vast industrial and military complex accountable only to the leader, at first complimented Rouhani on his speech to the UN General Assembly, in which he said Tehran was prepared to engage in "time-bound and results-oriented" nuclear talks, but then issued a coded warning.

"It was better that no time was given for a face-to-face meeting with Obama and he should have turned down a phone conversation until after the American government has shown its sincerity," Mohammad Ali Jafari, the head of the Islamic Revolutionary Guard Corps (IRGC), said.

Macho and wrong

It is perhaps not surprising that the IRGC, a force grown mighty on a mission to protect the Islamic Republic from its enemies, both internal and external, should balk at mending ties with the greatest of Iran's foes, the United States.

But Jafari's remark seemed to fly in the face of Rouhani's own coded message to the Guards only two weeks before.

"The IRGC is above and beyond political currents, not beside them or within them," the President had told the Guards. "The IRGC has a higher status, which is that of the whole nation."

In other words, he was telling them to stay out of politics.

The public comments of ministers, politicians and military commanders represent only a pale reflection of what is likely to be an intense debate within the largely opaque corridors of Iranian power, where policy is often arrived at by laboriously thrashing out a consensus, with Khamenei having the final word.

Rouhani, who took office in August, had the supreme leader's approval for his move to build bridges with Washington and gain some relief from sanctions that have fuelled inflation of more than 40 percent and led to a sharp fall in the value.

But by taking Obama's last minute phone call as he headed for the airport in New York, Rouhani may have over-stepped his remit from the ever cautious and deeply anti-Western Khamenei, according to some analysts.

"I think that Jafari's comments underscore the unscripted, improvised nature of Rouhani's conversation with Obama," said Dr Siavush Randjbar-Daemi, lecturer at Britain's University of Manchester. "It also gives some credence to Rouhani's claim that the Obama call was really an improvised initiative."

"Regarding Jafari, I think he too was taken aback by the speed with which events moved last week in New York, and sought to try to bring about a more moderate pace in the rapprochement process between Iran and the United States," he said.

With two weeks to go before the next round of nuclear negotiations in Geneva between Iran and the five permanent members of the UN Security Council - Britain, China, France, Russia and the United States - plus Germany, the debate within Iran appears to be intensifying.

"The Revolutionary Guards gave public support to Rouhani's trip to New York, but made clear that he has to negotiate from a position of strength," said Scott Lucas, an Iran expert and co-founder of EA Worldview which monitors Iranian media.

"Jafari's comments go further. This is a challenge for Rouhani to deliver on actual changes of US behaviour. 'Show us the progress', he's saying. He's testing Rouhani to see whether he can get some move forward from the US," he said.

More strident comments by Rouhani's foreign minister and chief nuclear negotiator Mohammad Javad Zarif on Tuesday appeared to show that Rouhani's government may be getting the message.

"President Obama's presumption that Iran is negotiating because of his illegal threats and sanctions is disrespectful of a nation, macho and wrong," he wrote on Twitter.

(Agencies)

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