The original plan was to kill Ismail Haniyeh, the political head of the Palestinian terror group, in May, when he attended the funeral of Ebrahim Raisi, Iran’s former President, reported British newspaper The Telegraph.

The operation didn’t go ahead due to the presence of large crowds inside the building and the high possibility of its failure, two Iranian officials told The Telegraph.

Instead, the two agents placed explosive devices in three rooms of the Islamic Revolutionary Guard Corp (IRGC) guesthouse in north Tehran where Haniyeh might stay, the British newspaper reported.

The agents were seen moving stealthily as they entered and exited multiple rooms within minutes, according to the officials who have CCTV footage of the building. The agents had reportedly moved out of the country but maintained a source in Iran.

At 2am on Wednesday, they detonated the explosives from abroad in the room where Haniyeh was staying, reported The Telegraph.

According to reports, Mossad and its director David Barnea recruited the agents from the Ansar al-Mahdi Protection Unit in Tehran.

“They are now certain that Mossad hired agents from the Ansar al-Mahdi protection unit,” an official within the IRGC told the Telegraph from Tehran, referring to an IRGC unit responsible for the safety of high-ranking officials.

He said: “Upon further investigation, they discovered additional explosive devices in two other rooms.”

A second official within the elite military forces of the IRGC told the Telegraph: “This is a humiliation for Iran and a huge security breach.”

The official said a working group had been established to come up with ideas to portray the assassination as not being a security breach.

“It’s still a question for everyone how it happened, I can’t make sense of it. There must be something higher up in the hierarchy that no one knows about,” he added.

There is now an internal blame game taking over the IRGC, with different sectors accusing each other of the failure, revealed the first official who spoke to The Telegraph.

Esmail Qaani, the commander of the IRGC Quds force said the breach had 'humiliated everyone'.

Who was Ismail Haniyeh?

Ismail Haniyeh was a Palestinian politician who was widely considered to be the chief political leader of Hamas, which has governed the Gaza Strip since 2007.

He was the chairman of the Hamas Political Bureau.

Mohammed Deif killed

Israel's army confirmed on Thursday that Hamas military chief Mohammed Deif was killed in an airstrike last month in the southern Gaza Strip, AFP reported.

The announcement followed reports from Hamas and Iran that the Palestinian movement's chief, Ismail Haniyeh, was killed in Tehran, though Israel has not commented on that claim.

"Mohammed Deif, the Osama bin Laden of Gaza, was eliminated on July 13," said Defence Minister Yoav Gallant.