UN Secretary-General Ban Ki-moon (L) meets with Iranian President Mahmoud Ahmadinejad in Tehran, Iran, on Aug. 29, 2012. The UN secretary general arrived here to attend the 16th Non-Aligned Movement Summit slated for Aug. 30 to 31. (Xinhua/Iran's Presidential Office)

Ban also told the Iranian leaders that Iran needed to take concrete steps to address the concerns of the International Atomic Energy Agency (IAEA) and prove to the world that its nuclear program is for peaceful purposes.

"He said there is no alternative, just diplomatic and negotiated settlement step by step based on reciprocity," Nesirky said. "Let me say the SG has made the same point on the nuclear question to the supreme leader."

The United States and its Western allies have long accused Iran of secretly developing nuclear weapons, but Tehran insists that its nuclear program is for civilian purposes only. The five permanent members of the UN Security Council (P5), Britain, China, France, Russia and the United States, plus Germany have held many rounds of negotiations with Iran on the issue, with no substantial progress achieved so far.

The Vienna-based IAEA has announced the establishment of an Iran Task Force, a separate team of nuclear experts, to inspect and investigate Iran's nuclear program, reports said on Wednesday.

"On Syria, the secretary-general urged the president and the supreme leader in their separate meetings to use Iran's influence to press on the Syrian leadership to urgently stop the violence and create a condition for a credible dialogue ... to meet the aspirations of the Syrian people," the spokesman said.

On the human rights, the secretary-general told the Iranian leaders that "the situation of human rights in Iran remains a source of concern."

Talking to reporters at a joint press conference with the Iranian parliament speaker in Tehran, the secretary-general said that Iran can play an important role in the peaceful settlement of the Syrian crisis, which broke out in March last year. Ban also hoped to see an Iranian role in the political settlement to the 18- month Syrian crisis, but his intention was blocked by Washington and its allies.

"We have discussed how (the) United Nations can work together with Iran to improve the human rights situation in Iran," Ban said at the joint press conference in Tehran. "We have our serious concerns on the human rights abuses and violations in this country. "