TEHRAN - The Organization of Islamic Cooperation (OIC) on Wednesday blamed Israel for an attack that killed Hamas political chief Ismail Haniyeh last week in Tehran, Iran’s capital.

A statement issued after an extraordinary meeting of the 57-member bloc in Saudi Arabia said the Muslim bloc “holds Israel, the illegal occupying power, fully responsible for this heinous attack”, which it described as “a serious infringement” of Iran’s sovereignty.

Gambia’s Foreign Minister Mamadou Tangara, whose country chairs OIC, said Haniyeh’s “heinous” assassination and the ongoing war in Gaza could lead to a regional conflict.

“The aggression and violation of the sovereignty and territorial integrity of the Islamic Republic of Iran by the assassination of a political leader on its soil is an act that cannot be viewed in isolation,” Tangara asserted, al Jazeera reported.

“This heinous act serves only to escalate the existing tensions potentially leading to a wider conflict that could involve the entire region.”

Iran and Palestine had called for the OIC meeting in the Saudi coastal city of Jeddah. The bloc represents the collective voice of the Muslim world.

Host Saudi Arabia also said Haniyeh’s assassination was a “blatant violation” of Iran’s sovereignty.

The kingdom’s deputy foreign minister, Waleed al-Khereiji, said his country rejects “any violation of the sovereignty of states or interference in the internal affairs of any country”.

Hamas and Iran have blamed Israel for Haniyeh’s killing in Tehran last week.

Iran has promised to retaliate, threatening “harsh punishment” for Israel.

"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,” Leader of the Islamic Revolution Ayatollah Ali Khamenei said in a statement hours after Haniyeh was assassinated. 

Speaking during Haniyeh’s funeral ceremony in Tehran last Thursday, Iranian Parliament speaker Mohammad Bagher Ghalibaf also said, "We will definitely act on the Leader's command to respond to the crime at the right time and place," noting the Israeli regime will pay a “heavy price” for this cowardly act.

Haniyeh was killed with a "short-range projectile" fired from outside his guesthouse in northern Tehran on July 31.