Iran on‌ Wednesday declared three days of mourning in memory of the head of the political bureau of the Palestinian resistance movement Hamas Ismail Haniyeh who was assassinated a day earlier in Tehran.

According to The Iran Project, following the assassination of the Hamas political chief, Iran will mark three days of public mourning across the country.

The Islamic Revolution Guard Corps (IRGC) announced in a statement on Wednesday morning local time that Haniyeh and one of his bodyguards were martyred in an attack on their residence in the Iranian capital.

The IRGC issued another statement hours later, stressing the assassination of Haniyeh showed that "the criminal, murderous and terrorist Zionist gang, without any regard for international rules, does not refrain from committing any criminal act to cover up the humiliating defeats of the 9-month war in the Gaza Strip".

"Undoubtedly, this crime by the Zionist regime will be met with a harsh and painful response from the powerful and great Resistance Front, especially Islamic Iran," it warned.

The message comes soon after Iranian President Massoud Pezeshkian and Supreme Leader of the Islamic Revolution Ayatollah Seyed Ali Khamenei vowed to retaliate against the Zionist regime.

Pezeshkian stressed that the assassination of Haniyeh will further consolidate the bond between the two nations, noting that the path of resistance will continue stronger than ever.

“The Islamic Republic of Iran will defend its territorial integrity, honor and dignity, and make the terrorist occupiers regret their cowardly act,” he warned.

Ayatollah Khamenei also warned Israel of a "harsh response" for the the assassination of Haniyeh, stressing it is the Islamic Republic's duty to avenge the blood of the Palestinian resistance leader.

“The criminal and terrorist Zionist regime martyred our dear guest in our homeland and left us bereaved, but it also set the ground for a harsh punishment for itself,” he warned.

The development came amid Hamas’ all-out endeavours to defend the Gaza Strip against an ongoing genocidal war by Israel, and the movement’s participation in negotiations aimed at bringing about a ceasefire to end the military onslaught against the besieged enclave.

Israel has been carrying out heavy bombardment across the Gaza Strip since early October 2023, responding to Al-Aqsa Storm, a retaliatory military operation staged by the blockaded territory’s resistance groups.

More than 39,000 Palestinians have been killed and nearly the entire population has been displaced. Over 90,000 people have also been wounded, according to health officials.

The figures exclude tens of thousands of dead who are believed to be buried in the bombed-out ruins of homes, shops, shelters, and other buildings.

The military campaign has turned much of the enclave of 2.3 million people into ruins, leaving most civilians homeless and at risk of famine.

Tel Aviv has also imposed a complete siege on Gaza, cutting off food, electricity, fuel and water supplies. The move has plunged the tiny territory into a humanitarian crisis.

Human rights organizations have warned that thousands of people in the besieged enclave are facing the risk of famine amid the ongoing Israeli devastating onslaught.

Iranian officials say the Palestinian people and the Gaza-based resistance movements have achieved a great victory while Israel suffered a “humiliating defeat” in its war on the coastal territory.

Gaza’s resistance groups have pledged to defend the coastal sliver with all their resources, asserting that it would be impossible to eliminate the resistance from the Palestinian territory’s rule.