Erdogan, who was greeted at the airport by Iranian Foreign Minister Ali Akbar Salehi, flew in from South Korea, where he had attended a nuclear security summit with other world leaders including US President Barack Obama.

He was accompanied by a large delegation that included the Turkish ministers for foreign affairs, energy, economy, and urban development and the environment.

Turkish intelligence and military officials, and the head of Turkey's Atomic Energy Organisation, Zafer Alper, were also with him.

Erdogan was to hold talks with Iranian President Mahmoud Ahmadinejad and parliamentary speaker Ali Larijani, IRNA said.

Dicussions were to concentrate on Iran's nuclear programme, the conflict in Syria, regional issues and bilateral relations, it said.

Turkey has proposed to host the next round of talks between Iran and the P5+1 group comprising the five permanent UN Security Council members plus Germany.

Those talks, expected to take place within weeks, carry hopes of defusing a tense international showdown over Iran's nuclear activities that has sent oil prices soaring.

Israel brandished the threat of possible military action, and the United States has never ruled out the option.

The last round of Iran/P5+1 talks, held in Istanbul in January 2011, collapsed.

Turkey, a NATO member that has agreed to host facilities for a missile shield that could be used against Iran, has refused to go along with Western sanctions on Iran that would curb vital oil imports from its neighbour.

The United States and Europe have been stepping up their pressure on Iran in an effort to get it to give up uranium enrichment, which they fear could be used in nuclear weapons they suspect Iran of researching.

Tehran has reacted defiantly by increasing enrichment and announcing other atomic progress, while insisting its nuclear programme is exclusively peaceful.

Kerry, who chairs the Senate's influential Foreign Relations Committee, led a hearing on US policy toward Iran and the options available to Washington as it reviews strategy over Tehran's nuclear ambitions ahead of a new round of talks April 13 between the Islamic state and world powers.

With concern rising over a possible Israeli military strike on Iran's atomic facilities, Kerry warned it was "certainly not realistic to expect that one high-level meeting is going to resolve all the differences or erase all of those decades of either misunderstandings or mistrust."

"To have any prospect of success, we need an approach that gives diplomatic engagement space to breathe, without allowing Iran to play for time and drag us into a drawn-out process," the senior Democrat said.

"It won't be easy to find a solution that might be acceptable to both sides, but also give the international community confidence that Iran neither has the capacity nor the desire to make a mad dash to nuclear weapons."

Former US undersecretary of state Tom Pickering told the hearing that foregoing diplomacy, negotiation and the use of sanctions in favor of a military strike on Iran could unleash a wave of terrorism against "soft American targets" worldwide.

"Iran or surrogates could attack businesses, non-governmental organizations, missionaries and virtually every American establishment in the region and beyond," said Pickering, a former ambassador to the United Nations as well as Russia, India and Israel.

He said hitting Iran's nuclear facilities would set back bomb-making capacity by a number of years, but it "has a very high propensity in my view of driving Iran into the direction of openly declaring and deciding... to make a nuclear weapon seemingly to defend itself," against further attack.

That would only heighten tensions in an already convulsive region, he said.

Instead, the United States and its allies should concentrate on negotiation.

A good starting point, Pickering said, would be Iran's earlier proposal that if they stop building up their uranium to 20 percent enrichment, the West would provide the fuel elements for the civilian Tehran Research Reactor.

"Ending 20 percent enrichment, which takes them halfway to the enrichment level for a bomb... would be a helpful step," he said.

Should Tehran then agree to turn over material it has enriched to 20 percent when the West delivers the fuel elements, "some freezing or easing of sanctions might be a fair quid pro quo for such steps."