According to the source, who had been briefed on the operation, the bomb was concealed about two months ago in the guest house where Haniyeh was known to stay in Tehran and detonated remotely once he was inside his room there.
The Iranian government and Hamas say Israel carried out the assassination. Israel has neither confirmed nor denied its involvement.
US officials were briefed on the operation by Israeli officials only after the assassination, the source said.
The New York Times was the first to report the details of Haniyeh’s assassination.
Haniyeh’s assassination raised fears once again that Israel’s conflict with Hamas and its allies could develop into a multi-front, fully-fledged war in the Middle East.
Iranian state media and Hamas previously indicated that Haniyeh was killed by a rocket fired from outside the building in which he was staying.
But the revelation that a bomb was smuggled inside the guest house, which was under the protection of Iran’s Islamic Revolutionary Guard Corps, indicates a startling breach of security for the IRGC.
It’s unclear when Haniyeh arrived in Tehran, but Iranian state media first reported that he would be flying in to attend the inauguration of the country’s new president on Monday. He had a full schedule of public appearances and meetings before he was assassinated, according to Iranian state media press reports.
Haniyeh was first pictured on Tuesday, before the inauguration, meeting with Iranian Supreme Leader Ayatollah Ali Khamenei. Afterwards, Iranian state media published images of Haniyeh meeting with Iran’s new President Masoud Pezeshkian. Haniyeh was next spotted arriving at the inauguration ceremony at Iran’s Islamic Consultative Assembly building, where he sat in the front row.
Just before 7:00 p.m. local time (11:30 a.m. ET), Haniyeh made his final public appearance at an exhibit at Tehran’s Milad Tower. At 2 a.m. that night, according to state media outlet IRNA, he was killed, with what IRNA described as an “airborne guided projectile.”
Iran’s Supreme Leader Ayatollah Ali Khamenei said Wednesday: “You killed our dear guest in our house and now have paved the way for your harsh punishment.”
His death marked the start of an unpredictable new phase of Israel’s war with Hamas, coming just hours on from an Israeli strike in Beirut, Lebanon, on Tuesday that killed Hezbollah commander Fu’ad Shukr, whom it blamed for a deadly attack in the Israeli-occupied Golan Heights over the weekend.
Israel on Thursday then announced it had confirmed it had killed Mohammed Deif, the head of Hamas’ military wing and a key architect of the October 7 attacks, last month.
Haniyeh’s coffin was moved through the streets of Tehran in a procession on Thursday, with thousands lining the streets to watch. He will be buried in Qatar’s capital Doha on Friday.