Prime Minister Recep Tayyip Erdogan, visiting Tehran, was expected to urge President Mahmoud Ahmadinejad Thursday to reverse his steadfast support of embattled Syrian President Bashar Assad, arguing that regime change in Syria was inevitable and inescapable, a senior Turkish official told Israel's English-language Ynetnews Web site.
The Turkish English-language newspaper Today's Zaman published a similar report.
The Erdogan-Ahmadinejad meeting was postponed to Thursday from Wednesday after Iran said Ahmadinejad had upper gastrointestinal bleeding.
Upper GI bleeding is normally considered a medical emergency requiring hospital admission. Tehran gave no further details about Ahmadinejad's condition or how it developed.
Erdogan was also scheduled to meet with Iranian supreme leader Ayatollah Ali Khamenei.
The meetings follow a statement from Iran's foreign minister that Tehran now backs U.N.-Arab League envoy Kofi Annan's peace plan for Syria.
The plan calls for talks between the opposition and the regime, a cease-fire and troop withdrawal, humanitarian assistance in areas hurt by the fighting, the release of people arbitrarily detained, free journalistic access and respect for "freedom of association and the right to demonstrate peacefully."
The plan does not require Assad to leave office.
Annan is scheduled to travel to meet with Iran leaders Monday or Tuesday.
Erdogan's meetings Thursday were to follow a nearly 2-hour meeting with Obama Sunday on ways of pressing Assad to step aside, including through non-lethal assistance to the opposition and urging Iran to end its support of Assad, U.S. and Turkish officials said.
Obama said after the meeting he and Erdogan agreed Syria must transition to a valid and rightful government after more than a year of deadly violence the United Nations says has killed more than 9,000 people.
Obama and Erdogan met in Seoul ahead of an international Nuclear Security Summit Monday and Tuesday.
Erdogan said Sunday taking action to protect Syrians within the limits of international law was a matter of conscience for Turkey.
Erdogan called on Assad to quit in November.
He met with U.S. CIA Director David Petraeus in Ankara, Turkey, March 13.
Turkey is sheltering tens of thousands of Syrian refugees who crossed the border in recent months fleeing the violence.
Turkey hosted a conference of Syrian dissidents Tuesday and is to host a "Friends of Syria" meeting of mostly Western and Arab countries Sunday to discuss a political transition and the opposition's vision for Syria, officials said.