(CNN) -- Israeli Prime Minister Benjamin Netanyahu says he would take a phone call from Iran's president, if he called, but warns that he would have tough words for the man he described this week as "a wolf in sheep's clothing."
"We're not averse to calling," Netanyahu said in an interview Thursday with CNN's Piers Morgan in New York.
"I'll tell you what I'll tell him," he said. "'You want the sanctions lifted? Stop your nuclear program.'"
Iranian President Hassan Rouhani, who took office in August, has projected a more moderate image than his predecessor, Mahmoud Ahmadinejad.
Western leaders have expressed optimism about Iran's more conciliatory tone under Rouhani, whose comments in recent weeks have raised hopes that a deal could be struck over the country's controversial nuclear program.
Rouhani has called for the lifting of international sanctions, imposed over the nuclear program, that have taken a heavy toll on the Iranian economy.
In an indication of the shifting mood, he spoke with U.S. President Barack Obama by phone last week, the first direct conversation between leaders of the two countries since the Iranian revolution in 1979.
The 15 minute conversation, which included translations, was described by Obama's National Security Advisor Susan Rice as "cordial and constructive."
Questions for Rouhani
But Netanyahu remains skeptical about Rouhani's intentions. In a speech at the U.N. General Assembly on Tuesday, he described him as "a wolf in sheep's clothing, a wolf who thinks he can pull the wool over the eyes of the international community."
He told Morgan on Thursday that he would have plenty of questions for Rouhani, including why Iran needs underground bunkers and intercontinental ballistic missiles.
"Why do you need to enrich uranium?" he asked, listing countries that operate civilian nuclear energy programs without enrichment, including Canada, Mexico and Indonesia.
"They don't have enrichment because enrichment -- uranium enrichment -- is how you make nuclear weapons," he said in the interview, which will air at 9 p.m. ET on Friday.
Iran has repeatedly insisted that its nuclear program is for peaceful purposes.
Khodadad Seifi, an Iranian representative at the United Nations, said this week that Tehran is cooperating with the U.N.'s nuclear watchdog, the International Atomic Energy Agency, and that its work is carried out under surveillance cameras.
Unperturbed by U.S. shutdown
Asked if he was concerned about the partial shutdown of the U.S. federal government this week, Netanyahu seemed unfazed.
"They'll work it out," he said. "Been there, done that."
And despite the crisis in Washington that has paralyzed many public services, Netanyahu defended the U.S. democratic system.
"I think, with all its flaws, the American political system has a lot riding for it," he said. "It's probably the best political system in the world."
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