Turkish Prime Minister Tayyip Erdogan arrived in Tehran on Wednesday for talks on Iran's nuclear programme amid strained relations between the two countries over the continuing bloodshed in Syria.
Erdogan will be meeting Iran's most powerful authority, Ayatollah Ali Khamenei, as well as President Mahmoud Ahmadinejad during his two-day visit.
Erdogan held talks about Iran with U.S. President Barack Obama on Sunday in South Korea, raising speculation Turkey was taking a message from Washington to Tehran - although a Turkish official dismissed that.
While Turkey has repeatedly voiced its support for Iran's right to establish a peaceful nuclear programme, it is at odds with Tehran over Syria where the government crackdown continues against opposition rebels and anti-government demonstrators.
Erdogan has urged Syrian President Bashar al-Assad to step down to end more than a year of fighting between Assad's forces and opponents of his rule. Turkey has also allowed opposition groups to meet regularly in Istanbul.
In contrast, Shi'ite Muslim Iran has steadfastly continued to support what is its closest Arab ally and whose leader is from the minority Alawite sect, an offshoot of Shi'ite Islam.
The Turkish official played down the issue of Syria, telling Reuters the talks would be smooth. They respect our leadership and our opinions. We have good cooperation with Iran and they know we are trying to bring stability to the region.
But a diplomat in Tehran said events in Syria had caused a lot of damage to relations and said many believed it was the most critical part of the visit.
There is a sense that Syria has become more important than the nuclear issue, the diplomat said. Iran doesn't accept Turkey's standpoint so it really depends on China and Russia. That might help Erdogan but he needs to do a lot of work.
China and Russia have given their backing to a U.N.-sponsored peace plan which calls for national dialogue but not the removal of Assad from office.
Obama said in Seoul there was time to resolve the dispute through diplomacy but the window was closing. Iran maintains it has the right to develop a peaceful nuclear programme but the U.S. and its allies suspect it has been trying to develop atomic weapons.
There is no new message on the nuclear issue, the Turkish official said. Turkey is not the messenger. That is just speculation. Our message is what we have said many times before.
Turkey has offered to host the next round of talks between Iran and the P5+1 group of countries which could take place as early as mid-April but a location has yet to be confirmed.
We have offered to host the meeting but it's not important where it takes place, only whether it is successful, the official added.
Iran is keen to maximise its economic cooperation with neighbouring Turkey as a way of minimising tough new sanctions imposed by the U.S. and the European Union against Iran's financial and energy sectors.
Turkey has been open to enhanced economic links but has been criticised for undermining the sanctions and last week failed to secure an exemption from Washington on its purchase of Iranian crude oil.
(Reporting By Marcus George)