U.S. President Barack Obama's chief of staff said on Sunday the election of Iranian President Hassan Rowhani was a "potentially hopeful sign," and that if he lived up to his obligation "to come clean on this illicit nuclear program, he will find a partner in us."

Speaking on CBS's "Face the Nation," Denis McDonough said: "If he (Rowani) is interested in, as he has said in his campaign, mending Iran's relations with the rest of the world, there is an opportunity to do that."

On Sunday, Israeli Prime Minister Benjamin Netanyahu urged the West not to let up pressure on Iran to curb its nuclear ambitions after the election of a new president widely seen as a moderate.

"We won’t fool ourselves, [and] the international community shouldn’t be tempted into wishful thinking and weaken the pressure on Iran regarding their nuclear program,” Netanyahu said of the election results.

Also on Sunday, Syrian President Bashar Assad said Damascus hopes to strengthen its ties with Tehran.

Syria's state-run SANA news agency said Assad also expressed determination to cooperate in all fields, "in the face of aggression, hegemony schemes and the attack on a national sovereignty in our region".

Iran is a key supporter of the Assad regime, which rebels are seeking to oust. Tehran also backs Hezbollah, the Lebanese Shiite group backing Damascus in the conflict that has claimed more than 92,000 lives by UN estimates.

SANA also quoted Prime Minister Wael al-Halqi as hailing Iran's presidential election was "a true reflection of real democracy" and thanking its people and leadership for their support to Syria.

Al-Halqi made the comments in a meeting in Damascus with Hassan Kazemi Qomi, an advisor in Iran's foreign ministry, the news agency said. He also stressed Damascus' desire to broaden relations with Tehran under the new leadership, SANA said.