UN chief Ban Ki-moon met Iran's president and supreme leader in Tehran on Wednesday to urge them to take concrete steps to prove the country's nuclear program is peaceful and to use their influence to help end Syria's 17-month conflict. Ban's spokesman Martin Nesirky said that in Ban's separate meetings with President Mahmoud Ahmadinejad and Supreme Leader Ayatollah Ali Khamenei, he further said their verbal attacks on Israel were offensive, inflammatory and unacceptable. Related articles: Khamenei: Israel will eventually disappear Op-ed: Trust our leaders on Iran Iranian ayatollah: Avoid war with Israel Ban arrived in Tehran on Wednesday for a three-day visit to attend a meeting of some 120 non-aligned nations. He defied calls from the United States and Israel to boycott the event. "He said Iran needed to take concrete steps to address the concerns of the International Atomic Energy Agency and prove to the world its nuclear program is for peaceful purposes," Nesirky, speaking from Tehran, told reporters in New York. Iran says its program is peaceful, but Western powers and their allies fear it is aimed at developing atomic weapons. Iran has been hit with four rounds of UN Security Council sanctions for refusing to halt its nuclear enrichment program. Khamenei said during the meeting that Iran was "working to allay the concerns regarding nuclear weapons. "The Americans know Iran is not interested in (developing) nuclear weapons. They are just looking for an excuse," he said. The supreme leader said nuclear weapons in Israel's hands poses a greater threat to the region. "I expect the UN to act on this issue," he said. Israel has never acknowledged having nuclear weapons but is widely believed to have a large arsenal. Following an earlier meeting with parliamentary speaker Ali Larijani, Ban told a press conference that "Iran can play an important role in solving the Syrian crisis peacefully," adding that "the Syrian people have suffered a lot ... with more than 20,000 dying in the past 18 months." 'Americans looking for an excuse.' Ban (L) with Khamenei Larijani, for his part, said "unfortunately, some big countries have acted adventurously in the region and have created disruption in the region like what we are witnessing in Syria." Iran, the chief ally of Syria's regime, accuses the United States, Turkey, Saudi Arabia and Qatar of sustaining the armed revolt in Syria. Addressing the Syrian crisis, Khamenei told Ban that the solution is to stop weapons shipments to the Syrian rebels, or as he put it, "irresponsible groups inside Syria," according to his website. A senior Iranian official gave details of the plan Iran is proposing at the summit. "Iran's proposal ... is a cease-fire and the implementation of a three-month mechanism for national reconciliation talks in this country," the official IRNA news agency quoted Deputy Foreign Minister Hossein Amir Abdollahian as saying Wednesday. Prime Minister Benjamin Netanyahu called the Non-Aligned Movement summit in Iran a "disgrace" to humanity. During a meeting Wednesday evening with the Prime Minister of Lower Saxony, Germany, David McAllister, the PM said "Seventy years ago, six million of our people were destroyed in an act of genocide. The world pledged ‘never again’ . . . It appears that many among the international community haven’t learned anything. I think this is a disgrace and a stain on humanity." Netanyahu said that the Iranian "regime denies the Holocaust and is working to destroy the Jewish state. This regime oppresses its people, takes part in the butchering of innocent Syrians, and calls for death to America, death to Israel." Reuters, AFP, AP contributed to the report Follow Ynetnews on Facebook and Twitter Receive Ynetnews updates directly to your desktop