Hamas’ top leader, Ismail Haniyeh, was killed in Iran, the group said.
In a statement released on Wednesday, Hamas said Haniyeh was killed in an Israeli attack on his residence in Tehran.
Several other senior Hamas figures, including Palestinian President Mahmoud Abbas, described Haniyeh’s death as an “assassination” and vowed to retaliate.
No one has yet taken responsibility.
The Iranian Revolutionary Guard Corps said the cause of the “incident” was not immediately clear but was “being investigated,” the AFP news agency reported.
According to the group, Haniyeh died after participating in the inauguration ceremony of the new Iranian president, Masoud Pezeshkian, who took office on Tuesday.
Hamas, the Palestinian group that controls Gaza, said Haniyeh was “killed in a treacherous Zionist attack.”
The group’s political cabinet member, Musa Abu Marzuk, said it was a “cowardly act” and that “it will not go unanswered”; while another senior Hamas official, Sami Abu Zuhri, said the group “will continue on its path.”
“This assassination of brother Haniyeh by the Israeli occupation is a serious escalation that aims to break the will of Hamas and the will of our people and achieve false goals,” Sami Abu Zuhri told the Reuters news agency.
Israel has not yet responded or issued a statement.
Haniyeh, 62, was widely considered the overall leader of Hamas.
He was a prominent member of the group’s movement in the late 1980s and was imprisoned by Israel for three years in 1989 while it suppressed the first Palestinian uprising.
He was then exiled in 1992, in a no man’s land between Israel and Lebanon, along with several Hamas leaders.
Haniyeh was appointed Palestinian prime minister in 2006 by President Mahmoud Abbas after Hamas won the most seats in national elections, but was dismissed a year later after the group ousted Abbas’s Fatah party from the Gaza Strip in a week of deadly violence.
Haniyeh rejected his dismissal as “unconstitutional”, stressing that his government “would not abandon its national responsibilities to the Palestinian people” and continued to govern in Gaza.
He was elected head of Hamas’s political bureau in 2017.
In 2018, the US State Department designated Haniyeh a terrorist. He has lived in Qatar for the past few years.