Tehran, Iran - 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 southern Beirut, killing a senior commander of the Hezbollah 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 headquarters 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.

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"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' Sepah news website.

The Guards said the cause of the incident was not immediately clear but it was "being investigated."

Haniyeh had traveled to Tehran to attend Tuesday's swearing-in ceremony of Iranian President Masoud Pezeshkian.

The Israeli army declined to comment on foreign media reports.

Haniyeh was elected head of the Hamas political bureau in 2017 to succeed Khaled Meshaal. He was already a well-known figure, having become Palestinian prime minister in 2006 following an upset victory by Hamas in that year's parliamentary election.

Considered a pragmatist, Haniyeh lived in exile and split his time between Turkey and Qatar. He had traveled on diplomatic missions to Iran and Turkey during the war, meeting both the Turkish and Iranian presidents.

Haniyeh was said to maintain good relations with the heads of the various Palestinian factions, including rivals to Hamas.

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He joined Hamas in 1987 when the group was founded amid the outbreak of the first Palestinian intifada, or uprising, against Israeli occupation, which lasted until 1993.

Palestinian President Mahmud Abbas said Wednesday the killing of Haniyeh was a "cowardly act" and urged Palestinians to remain united against Israel.

"President Mahmud Abbas of the State of Palestine strongly condemned the assassination of Hamas leader Ismail Haniyeh, deeming it a cowardly act and a serious escalation," Abbas' office said in a statement. "He urged our people and their forces to unite, remain patient, and stand firm against the Israeli occupation."

Israel has killed at least 39,400 people in Gaza since October, according to the territory's health ministry. Israeli soldiers and settlers have killed hundreds of Palestinians in the West Bank in that same time period.