Turkish President Recep Tayyip Erdoğan on Wednesday held a phone conversation with the wife and children of Hamas chief Ismail Haniyeh.
During the conversation, Erdoğan expressed his "deep sorrow" over Haniyeh's killing in a "treacherous" assassination in Tehran.
Haniyeh, a prominent Palestinian leader, was reportedly targeted while in Iran, prompting widespread condemnation from many quarters.
Hamas announced early Wednesday that Haniyeh was killed in an Israeli airstrike on his residence in the Iranian capital Tehran.
The Iranian state television also reported Haniyeh's death, noting that an investigation into the assassination is ongoing and that the results will be announced soon.
Israel has made no immediate announcement about the assassination.
