A senior Hamas official said Wednesday that the killing of the Palestinian movement's chief Ismail Haniyeh "will not go unanswered".
"The assassination of leader Ismail Haniyeh is a cowardly act and will not go unanswered," Hamas political bureau member Musa Abu Marzuk said in a statement.
Hamas said Wednesday its political leader, Ismail Haniyeh, was killed in an Israeli strike in Iran, where he had been attending the inauguration of the country's new president.
Haniyeh's killing came after Israel on Tuesday struck a Hezbollah stronghold in southern Beirut, killing a senior commander of the Iran-backed group it said was responsible for a weekend rocket attack on the Israel-annexed Golan Heights.
"Brother, leader, mujahid Ismail Haniyeh, the head of the movement, died in a Zionist strike on his residence in Tehran after he participated in the inauguration of the new (Iranian) president," the Palestinian group said in a statement.
Iran's Revolutionary Guards also announced the death, saying Haniyeh's residence in Tehran was "hit" and he was killed along with a bodyguard.
"The residence of Ismail Haniyeh, head of the political office of Hamas Islamic Resistance, was hit in Tehran, and as a result of this incident, him and one of his bodyguards were martyred," said a statement by the Islamic Revolutionary Guard Corps's Sepah news website.
The Guards said the cause of the incident was not immediately clear but it was "being investigated."
Haniyeh had travelled to Tehran to attend Tuesday's swearing-in ceremony of Iranian President Masoud Pezeshkian.
The Israeli army declined to comment on foreign media reports.
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