Iran has claimed that the assassination of Hamas political leader Ismail Haniyeh in Tehran earlier this week was carried out by a “short-range projectile” and a “severe explosion” outside a guest house where he was staying.

The death of the Hamas leader further heightened tensions at an already volatile time, raising fears that Israel’s conflict with Hamas and its allies could develop into a multi-front, fully-fledged war in the Middle East.

The Iranian government and Hamas say that Israel carried out the assassination. Israel has neither confirmed nor denied its involvement.

On Saturday, Iran warned that “blood vengeance” for the killing was “certain.”

The Islamic Revolutionary Guard Corps (IRGC) claimed in a statement that the short-range projectile that reportedly killed Haniyeh had a warhead of about seven kilograms, based on “investigations and research conducted.”

US officials were briefed on the operation by Israeli officials only after the assassination, the source said.

“This action was planned and executed by the Zionist regime with the support of the criminal American government,” the IRGC alleged. Iran calls Israel the Zionist regime.

Israel “will decisively receive the response to this crime,” which is a “severe punishment” that will come at “an appropriate time, place, and manner,” the IRGC said.

The chief spokesperson for the Israel Defense Forces (IDF), Rear Admiral Daniel Hagari, said Thursday that Israel is on “high alert” for both defensive and offensive military action.

“IDF forces are deployed in the air, at sea and on the ground, and are prepared for all scenarios, especially for offensive plans within the immediate timeframe,” Hagari said.