Qatar's Emir Sheikh Tamim bin Hamad Al Thani is the first national leader to visit the Iranian capital since the US killing of Iranian General Qassem Soleimani a little more than a week ago.
Sheikh Tamim said talks were the only way forward in the crisis between Iran and the US.
Protesters have come out onto the streets across Iran for a second day, after Iranian officials admitted the military accidentally shot down a Ukrainian airliner.
But there have also been rallies against the UK after Iran briefly arrested the British ambassador for attending what he described as a vigil for the people killed in the Ukraine plane crash.
Al Jazeera's Dorsa Jabbari reports from Tehran.