The leader of the Palestinian resistance group was killed last Wednesday during a visit for the swearing-in ceremony of Iranian President Masoud Pezeshkian.

The "necessary investigations" have begun and the results will be announced "as soon as the probe is completed," said judiciary spokesman Asghar Jahangir.

"Until today, no arrests have been made in connection with this case," he said, adding that the investigations involved Iranian military officials.

Iran's Revolutionary Guards said Haniyeh was killed using a "short-range projectile" launched from outside his accommodation in Tehran.

Iran and Hamas have blamed Israel and vowed to retaliate. Israel has declined to comment.

On Saturday, the New York Times reported that Iran had arrested more than two dozen people, including senior intelligence officers among others, in connection with Haniyeh's killing.

Jahangir dismissed the claims about any arrests as "rumours" and "false".

"Haniyeh's assassination will definitely be met with a courageous response by the Islamic Republic," he said.

Haniyeh's death came hours after an Israeli strike in south Beirut killed a senior commander of Hezbollah, the Lebanese militant group that Israel blamed for a deadly rocket strike on the Israeli-annexed Golan Heights.

The two high-profile killings are the latest of several major incidents that have inflamed regional tensions during the Gaza war, which has drawn in Iran-backed militant groups in Syria, Lebanon, Iraq and Yemen.

Late Monday, Pezeshkian said Israel would "receive the response for its crimes and arrogance," but insisted that Tehran "is in no way seeking to expand the scope of war and crisis in the region".