Just a year ago, Turkey and Iran were deep in a heated exchange over their opposing roles in the Syrian war and sectarian conflicts that are shredding the Middle East.

Turkey’s President Recep Tayyip Erdoğan accused Iran of fighting the self-described Islamic State “only to take its place,” and said Iran’s aim to dominate the region was “not possible to tolerate.”

Iran’s Foreign Minister Mohammad Javad Zarif fired back, accusing Turkey’s leaders of causing “irreparable damage from their own strategic mistakes.”

Yet today, Turkey and Iran are engineering a partial rapprochement, an effort that was on display as Iran’s President Hassan Rouhani arrived in Istanbul for an April 14-15 summit of the Organization of Islamic Cooperation (OIC). Setting aside the strategic chasm of the Syrian conflict, the two powers are keen to revitalize a multitude of commercial and other ties and to shed the isolation both have confronted – Iran over its nuclear program, and Turkey from disputes with many of its neighbors.

Even a slight healing of wounds here could impact for the better the Sunni-Shiite divide across the region, and a string of regional proxy wars.

“Syria itself is a huge, divisive issue. But we aren’t talking about any two countries X and Y, we are talking about two countries with long and deep experience of statehood that have lived for centuries in the same neighborhood,” says Mustafa Kibaroğlu, head of the Center for International Security Studies and Strategic Research at MEF University in Istanbul. “So [Syria] is a major issue, but it is not the only issue,” says Mr. Kibaroğlu.

Inking deals

Reaching this point has not been easy: As recently as December, Erdoğan warned Iran that comments about Turkey’s role in trading oil for the Islamic State – something Turkey denies – would “cost them a huge price.” But in recent weeks Turkish Prime Minister Ahmet Davutoğlu visited Tehran, while Iran’s Foreign Minister Zarif has been in Turkey this week. The two countries have inked numerous deals, from lowering customs, banking, and transport barriers to setting up a $350 million credit line, Iranian media report. Deals were also done on stock exchange cooperation and boosting electricity provision from Iran as well as oil and gas sector investments from Turkey.

The aim is to triple trade to $30 billion per year, officials from both sides say, especially after the mid-2015 nuclear deal between Iran and six world powers led to sanctions being partially lifted from Iran in January.

On the diplomatic front, the two regional heavyweights are vowing to be more in the same corner in battling terrorism and sectarian divides. While analysts note that Mr. Erdoğan’s welcome to the OIC has been especially ingratiating for Saudi Arabia’s King Salman – a staunch supporter of Turkey’s bid to topple Iran’s Syrian ally President Bashar al-Assad – ties with Iran are also fundamentally important.

The summit – with its elaborate official dinners aboard the presidential yacht in the Bosphorus and at Ottoman-era palaces – marks a moment when leaders of Shiite Iran and Sunni Saudi Arabia will be under the same roof, despite waging proxy conflicts for influence from Yemen and Iraq to Syria and Lebanon. Earlier this month in Washington, Erdoğan said Turkey could be the “best mediator” between the rival powers.

Yet a draft statement for the summit has already sparked controversy, with Mr. Zarif on April 13 accusing Saudi Arabia of “destructive” moves by trying to insert language against Iran and its Lebanese Shiite ally Hezbollah and Mr. Rouhani today rejecting such “divisive moves.”

But there is lower-hanging fruit that may boost Turkey-Iran ties.

“Iran and Turkey have a hundred reasons to cooperate and few to not,” says Kayhan Barzegar, director of the Institute for Middle East Strategic Studies in Tehran.

“The Syrian crisis artificially put Iran and Turkey in opposite regional positions,” says Mr. Barzegar. “There are a lot of traditional common geopolitical interests such as dealing with terrorism and extremism.... So they take advantage of any opportunity to return to their natural and normal relation, which is continued cooperation.”

Neither side is likely to budge over divergent views of the fate of Mr. Assad. United Nations peace talks to end five years of war in Syria resumed this week in Geneva.

Still, “there exists political will on both sides to remove barriers and develop relations,” said Mahmoud Vaezi, an Iranian minister and Rouhani’s special representative for Turkish affairs, last week.

Mr. Vaezi said Turkey is the first country that created and shares a formal “supreme council of cooperation” with Iran, and that Rouhani would attend its third session this week.

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“While both countries are consistent about their Syria policy, mostly due to different views in dealing with threats, their mutual needs to strengthen state-to-state relations will consistently keep them together,” says Barzegar in Tehran. “They have learned in the course of contemporary history how to respect each others’ interests and principles.”

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