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Iranian President Hassan Rouhani on Saturday called on Recep Tayyip Erdoğan to take united stance against Washington following the killing of Iranian General Qassem Soleimani by a U.S. air strike on Friday.

Describing the killing of Soleimani as a grave mistake, Rouhani during a phone call with Erdoğan said that silence in the face of such aggression would embolden the United States, Sözcü newspaper reported.

"If we do not take a unanimous stance against the U.S.' mistakes, a great danger will threaten our region,” Rouhani said.

"Iran and Turkey have always negotiated on complicated matters,” he added.

According to the Russian news agency RT, Erdoğan expressed his "regret" for the loss of Iranian general Qassem Soleimani on the phone, calling him a “martyr”. He also reportedly said he understood the anger of Iran’s people and leaders. He also reportedly expressed his distaste for external interference, which he said destabilizes the region.

Erdoğan discussed regional developments and bilateral relations in phone calls with his Iranian and Iraqi counterparts on Saturday, state-run Anadolu news agency reported.

Erdoğan’s phone call with Iran's Rouhani and Iraq's Barham Salih arrives after Ankara expressed concern about rising tensions between the United States and Iran following the killing of Soleimani.

The Turkish president on Friday led a security meeting to discuss latest developments in the Middle East, following the U.S. air strike in Baghdad that killed the commander of Iran’s elite Quds Force.