Why did Rouhani tout Iran's nuclear program after returning from US?

Upon landing in Iran following his diplomatic "charm offensive," the Iranian president was greeted by support but also had to dodge tossed eggs and shoes and bear criticism from Iran's Revolutionary Guard.

Iranian President Hassan Rouhani at the UN 370 (photo credit: REUTERS/Brendan McDermid)
Iranian President Hassan Rouhani at the UN 370
(photo credit: REUTERS/Brendan McDermid)
The smile on the face of Iranian President Hassan Rouhani came off his face at about the same time that he landed at the airport in Tehran. 
Next to the hundreds of supporters of his "charm offensive" at the airport were dozens of young Iranians who support the conservative stream of politics in the Islamic Republic. These young conservatives threw shoes and eggs at the president in protest of his warming of relations with the West and especially the telephone call that Rouhani had with US President Barack Obama.
On Tuesday the Iranian parliament expressed its confidence in Rouhani's new diplomacy with 230 of 290 members of the Majles voting in favor of the resolution.
But alongside this resolution of support, voices of dissent were also heard from parliament especially with regard to Rouhani's telephone conversation with Obama. Speaker of the Iranian parliament Ali Larijiani for example hailed Rouhani's diplomacy but conspicuously omitted  any mention of the Obama phone call.
Beyond the small public protest at the airport and the odd critical discussion in parliament, Rouhani should be concerned about the rare public statements made by the Iranian Revolutionary Guard.
General Mohammad Ali Jafari made clear that the President should have refused receiving Obama's call. Jafari is considered one of the most powerful figures and a close confidant of Supreme Iranian leader Ayatollah Khamenei. 
It is understandable that it would have been difficult for Rouhani not to speak to Obama. Just the day before he refused to meet with the US president. The Iranian Foreign Minister Mohammad Javad Zarif said that the White House tried five times to set up the call between the US and Iranian leaders until the two finally spoke. 
It may be that Rouhani believed that speaking to Obama would positively impact his attempts at convincing the West to ease economic sanctions against Iran.
The problem that he faces is that there are a number of people at home, most notably the leadership of the  Revolutionary Guard that carefully and watch each step that Rouhani takes with suspicion.
For his opponents in Iran, his smiling charm offensive which was received in Israel skeptically, is exaggerated and will end up harming the Iranian nuclear program.
So it is no surprise that two days after returning home, Rouhani and the people close to him were already sounding more cautious with regard to negotiations on Iran's nuclear program and were especially adamant about refusing to cease the enrichment of uranium on Iranian soil.