TEHRAN, Aug. 1 (Xinhua) -- Mournful people from different walks of life in the Iranian capital Tehran on Thursday held a funeral procession for Hamas Politburo Chief Ismail Haniyeh, who was killed in an alleged Israeli attack a day before.

The ceremony officially began at 8:00 a.m. local time (0430 GMT) at the University of Tehran, where Iran's Supreme Leader Ali Khamenei led the funeral prayers for the Hamas chief and his security guard, who was killed in the same attack.

The funeral prayers were attended by many top Iranian commanders and officials, including President Masoud Pezeshkian, Parliament Speaker Mohammad Baqer Qalibaf and Judiciary Chief Gholamhossein Mohseni-Ejei, as well as a large number of mourners.

People attend the funeral procession of assassinated Hamas politburo chief Ismail Haniyeh in Tehran, Iran, on Aug. 1, 2024. (Xinhua/Shadati)

Prior to the prayers, Qalibaf extended condolences over the tragic incident, saying, "It is our duty to respond (to Haniyeh's assassination) at the appropriate place and time."

Israel would pay a "heavy price for its cowardly attack against Iran's secure territory," Qalibaf stressed.

Following the prayers, Khamenei met Haniyeh's children and Hamas officials.

During the procession, a huge number of Iranians, including top officials and military commanders, accompanied the Hamas leader's body from the University of Tehran to the iconic Azadi square in central Tehran, while chanting slogans in condemnation of Israel and the United States, holding pictures of Haniyeh, Iran's leader and General Qassem Soleimani, the top Iranian commander who was killed in an attack by the United States in Iraq in January 2020, and waving Iranian and Palestinian flags.

People attend the funeral procession of assassinated Hamas politburo chief Ismail Haniyeh in Tehran, Iran, on Aug. 1, 2024. (Xinhua/Shadati)

Speaking to reporters during the procession, the Iranian officials said that Israel would definitely be punished for its "act of terror."

Tehran Mayor Alireza Zakani said Israel would certainly receive a far "stronger slap" compared to the one Iran delivered to it on April 14 in response to an Israeli attack on the Iranian consulate in Syria earlier that month, according to the official news agency IRNA.

At the end of the ceremony, which lasted for four hours, the Iranians bade a final farewell to the Hamas leader before the transfer of his body to the Qatari capital Doha to be laid to rest.

People attend the funeral procession of assassinated Hamas politburo chief Ismail Haniyeh in Tehran, Iran, on Aug. 1, 2024. (Xinhua/Shadati)

Haniyeh, who had been invited to attend the swearing-in ceremony of the Iranian president on Tuesday, was killed along with his bodyguard early Wednesday when their residence in Tehran was hit.

Iran accused Israel of carrying out the assassination while Israel has yet to confirm its involvement.