Iran's Revolutionary Guards said Wednesday that the chief of the Palestinian militant group Hamas, Ismail Haniyeh, was killed in Tehran along with one of his bodyguards.

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

Haniyeh arrived in Tehran on Tuesday to attend the inauguration of Iran's new President Masoud Pezeshkian in parliament.

He had met with Pezeshkian as well as Iran's supreme leader Ayatollah Ali Khamenei.

Tuesday's swearing-in ceremony came amid concerns of war between Israel and Lebanon's Hezbollah following a Saturday rocket attack on the Israeli-annexed Golan Heights.

Israel has accused Hezbollah of responsibility for the attack that killed 12 children, but the Iran-backed Lebanese group has denied any involvement.

Later on Tuesday, Israel struck Hezbollah's stronghold in southern Beirut in retaliation for the Golan strike, saying it had killed the commander responsible for the attack.

A source close to Hezbollah said Shukr was the target but that he "survived the Israeli strike". AFP was not immediately able to confirm that report.

Iran, which does not recognise Israel and considers it to be its arch-foe, has repeatedly warned Israel against attacking Lebanon.

"The Zionist regime (Israel) will make a great mistake with heavy consequences if it attacks Lebanon," Pezeshkian said during a Monday call with French President Emmanuel Macron, according to the Iranian president's website.

Regional tensions have soared since the start of the Israel-Hamas war in October, drawing in Iran-backed militant groups in Syria, Lebanon, Iraq and Yemen.

The October 7 Hamas attack on southern Israel that started the war resulted in the deaths of 1,197 people, mostly civilians, according to an AFP tally based on official Israeli figures.

Militants also seized 251 hostages, 111 of whom are still held captive in Gaza, including 39 the military says are dead.

Israel's retaliatory military campaign in Gaza has killed at least 39,400 people, according to the health ministry in the Hamas-run territory, which does not provide details on civilian and militant deaths.

Iran has made support for the Palestinian cause a centrepiece of its foreign policy since the 1979 Islamic revolution.

It has hailed Hamas's October 7 attack on Israel but denied any involvement.