UN leader Ban Ki-moon will stress to Iranian leaders this week that they must take "urgent" action on the country's nuclear drive and human rights, a UN spokesman said.
The warning was given as Ban headed for Tehran to take part in the Non-Aligned Movement summit starting Wednesday. The United States and Israel said that Ban should not go to Iran.
The UN secretary general will raise the "clear concerns and expectations of the international community on the issues for which cooperation and progress are urgent for both regional stability and the Iranian people," a UN spokesman Farhan Haq told reporters.
"These include Iran's nuclear program, terrorism, human rights and the crisis in Syria," the spokesman added.
Ban expect to meet Iran's supreme leader Ayatollah Ali Khamenei and President Mahmoud Ahmadinejad. He arrives in Tehran on Wednesday and leaves again on Friday.
The UN leader has called on Iran, which faces UN sanctions over its nuclear drive, to prove that its research is peaceful. He has also slammed recent remarks by the supreme leader and Ahmadinejad calling Israel a "cancerous tumor."
The United States and European powers say that Iran is seeking to build a nuclear bomb and has sought to increase international pressure. Iran insists it wants nuclear power for peaceful purposes.
Ban has also been urged by human rights groups to take a stand on conditions in the country, which makes extensive use of capital punishment and has also been accused of persecuting political opponents and ethnic minorities.
"It is clear that when he goes there that he will reiterate his concern that the overall human rights situation in Iran remains critical," Haq said.
"And while his program is not yet finalized, he will be directing his message to all segments of Iranian society and the political spectrum.
"Regarding the message on human rights, Iran has an obligation under international law to protect freedom of peaceful assembly, association and expression and allow greater space for media activists, human rights defenders and political activists," the spokesman said.