A prominent Hamas leader, Ismail Haniyeh has been killed in an Israeli raid on his residence in Tehran.
The news was confirmed in a statement released on Wednesday.
According to Hamas group, Haniyeh died after participating in the inauguration ceremony of the new Iranian president Masoud Pezeshkian who was sworn in on Tuesday.
The Iranian Revolutionary Guard Corps said the cause of the "incident" was not immediately clear but was "being investigated", AFP news agency reported.
Haniyeh, 62, was a prominent member of the Hamas movement in the late 1980s.
Israel imprisoned Haniyeh for three years in 1989 as it cracked down on the first Palestinian uprising.
He was then exiled in 1992 to a no-man's-land between Israel and Lebanon, along with a number of Hamas leaders.
Haniyeh was appointed Palestinian prime minister in 2006 by President Mahmoud Abbas after Hamas won the most seats in national elections, but he was dismissed a year later after the group ousted Mr Abbas' Fatah party from the Gaza Strip in a week of deadly violence.
Haniyeh rejected his sacking as "unconstitutional", stressing that his government "would not abandon its national responsibilities towards the Palestinian people", and continued to rule in Gaza.
He was elected head of Hamas's political bureau in 2017.
In 2018, the US Department of State designated Haniyeh a terrorist. He had lived in Qatar for the past several years.