Since sanctions are the West's reaction to Iran's nuclear program and the cause of its economic difficulties, Rouhani has to take measures that would prompt the West to ease, if not lift, those sanctions. For this, Rouhani has to show flexibility in Iran's uranium enrichment policy.

In fact, Rouhani is adept at dealing with Western countries on the nuclear issue. As Iran's top nuclear negotiator from 2003 to 2005 under former president Mohammad Khatami, Rouhani and his team reached an agreement with the United Kingdom, France and Germany on a peaceful solution to the Iranian nuclear issue. At that time, Teheran had agreed to suspend its uranium enrichment program to ease international pressure.

In the course of his presidential campaign and after winning the election, Rouhani has pledged to improve relations with the international community, hoping to mend ties with Western countries to break Iran's international isolation. He has even promised to restore diplomatic ties with the US, which severed relations with Iran after the 1979 revolution and seizure of the US embassy by Islamic students.

Encouragingly, the White House has responded by saying that it was ready to engage with the new Iranian government on the diplomatic level to break the stalemate in the nuclear talks.

It is heartening to see Iran and the international community both make goodwill gestures to resume negotiations on the Iranian nuclear issue. But the issue will still be difficult to resolve because the fundamental differences between Teheran and the West hardly seem to be narrowing. At least in the short term, we should not expect any substantial breakthrough.

Another tough diplomatic challenge facing Rouhani is how Iran should respond to the Syrian crisis.

The US administration, claiming that the Bashar al-Assad government has used chemical weapons in Syria's civil war, has decided to broaden its aid, including military support, to Syrian opposition groups. And Egyptian President Morsi Mohamed has decided to cut off diplomatic relations with Damascus and urged Western powers to impose a no-fly zone on Syria.

So it is likely that as a strategic ally of Syria, Shiite Iran will wholeheartedly support the Bashar al-Assad government, and continue to strive for regional leadership and try to influence Saudi Arabia and other Sunni-ruled Islamic countries by playing an important role in the Syrian crisis.

The author is a senior fellow at the Chahar Institute and a researcher at the Institute of West Asian and African Studies, affiliated to the Chinese Academy of Social Sciences.