Annan is scheduled to meet with Iranian Foreign Minister Manuchehr Mottaki and the secretary of Iran's Supreme National Security Council, Ali Larijani, who is also Iran's chief nuclear negotiator.
The UN secretary-general is due to meet President Mahmud Ahmadinejad on September 3.
Annan, who has been on a weeklong trip to the Middle East to bolster the Lebanon truce, arrived in Tehran from Syria.
Iran and Syria are seen as the main backers of Hizballah, the target of the Israeli military campaign. But on his last stop -- in Damascus on September 1 -- Annan said President Bashar al-Assad had pledged Syrian help in enforcing the Lebanon cease-fire by working to prevent arms smuggling across its border to Hizballah.
Annan will be keen to receive Iranian support for that endeavor as well during his meetings in Tehran.
But the nuclear issue will also be at the top of their agenda, following Iran’s failure on August 31 to meet a UN deadline to suspend its enrichment of uranium.
Missing the deadline opens the door to possible UN sanctions, an issue the United States has urged the Security Council to tackle.
John Bolton, America’s UN envoy, said on September 1 that U.S. President George W. Bush "has been very emphatic that it is unacceptable for Iran to have nuclear weapons."
Ahmadinejad on September 1 reiterated that Iran has no intention of giving up its right to peaceful nuclear technology.
In an interview with RFE/RL's Radio Farda, Gregory Schulte, the U.S. ambassador to the IAEA, said the United States "strongly [supports] the peaceful use of nuclear technology, including by Iran." However, he said that that Iran's uranium enrichment activities "are not necessary for civil nuclear power" and that "after three years of intensive verification work" the head of the IAEA, Muhammad el-Baradei, "cannot certify that Iran's nuclear program is peaceful."
So far, the United States has failed to convince all veto-wielding members of the UN Security Council that sanctions are necessary.
Russia and China have dismissed any talk of sanctions, and the European Union on September 1 stated that it is too early to impose sanctions on Iran for its failure to heed the UN.
But EU foreign policy chief Javier Solana noted that Iran does not have an "indefinite" period of time to resolve the standoff.
Annan's challenge in Tehran will be to keep that pressure on Iran, while seeking a diplomatic solution to the crisis.
Comprehensive sanctions could further slow development in Iran's strategic oil and gas sectors (Fars)
WHAT DOES TEHRAN REALLY THINK? On August 22, Radio Farda correspondent Fatemeh Aman spoke with Alex Vatanka, Eurasia editor for Jane's Information Group, by telephone from Alexandria, Virginia. Vatanka discussed the possible impact that comprehensive sanctions could have for Iran.
Radio Farda: Some Iranian authorities are trying to create the impression that they aren't concerned about the possibility of international sanctions against it. They emphasize that what Iran has achieved so far has happened despite the sanctions already in place against it. Are they really not afraid of sanctions?
Vatanka: I think that what the Iranians are trying to do is to continue to play this balancing act. On the one hand, they are trying to say, "Look, we have done without you for 27 years; we can continue." On the other hand, if you look at every other major Iranian overture toward the U.S., obviously what they are hoping to do is remove those sanctions. It is the sanctions that have been the biggest obstacle to a genuine expansion in the Iranian economy. It is the sanctions and U.S. policies vis-a-vis Iran that have, for instance, kept Iran from joining the World Bank. It is sanctions and so on that have made the Iranian oil industry have such a tough time in bringing investment into the strategic oil and gas sectors. People like [former Iranian President Ali Akbar Hashemi-]Rafsanjani back in the mid 1990s even kept certain fields untouched because the idea was that U.S. companies should have those once the sanctions were lifted.
I think sanctions are quite important to the Iranians, but at the same time what they are trying to say is, "Don't assume that we are going to fall off our chair just because you mentioned the sanctions card." It is part of a kind diplomatic chess game going on by Tehran. But remember if we look and listen to Iranian reformists, this is being openly debated inside Iran. The question that is being asked of [President Mahmud Ahmadinejad and his entourage] is, "What is the ultimate objective?" Is it just Islamic independence? Is it just the ability to enrich uranium? The debate in Iran by the reformists -- and I think a lot of people would sympathize with this -- is, "What are we being sanctioned for exactly and what policies do you have to make sure that those sanctions don't hit us harder than we have already been hit?"
Remember, the big issue here is this: Iran has been sanctioned by the U.S. Iran has never faced comprehensive United Nations sanctions. The Iranian people have never suffered on a scale that the Iraqi people, for instance, suffered because of such sanctions. So it is kind of disingenuous of these senior leaders to pretend that Iran has already gone through comprehensive sanctions. Iran has not. And it will be totally different set of circumstances that will have a totally different impact on Iranian society and the economy, should the UN impose comprehensive sanctions on the country.
THE COMPLETE PICTURE: RFE/RL's complete coverage of controversy surrounding Iran's nuclear program.
An annotated timeline
of Iran's nuclear program.