Ismail Haniyeh, pictured at a press conference in Tehran in March, was killed in the city after attending the inauguration of the new Iranian president.
Haifa, Israel CNN  — 

Hamas political leader Ismail Haniyeh was assassinated in Tehran on Wednesday using an explosive device that had been covertly hidden in the guest house where he was staying, a source familiar with the matter told CNN.

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.

CNN has sought comment from the Iranian government.

An image published by the New York Times shows the building where Haniyeh is believed to have been assassinated. A corner of?the building is now covered with a green cloth.?Apparent debris also litters the ground floor roof of the building, directly underneath the green cloth.

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.”

Haniyeh’s body arrived in Doha on Thursday from Iran in preparation for his burial on Friday, videos obtained by CNN show.

According to Hamas and Qatari state media, Haniyeh’s funeral prayer will be held after the Friday prayer at the Imam Muhammad ibn Abd al-Wahhab Mosque in the Qatari capital, followed by the burial at the Imam Founder Cemetery in Lusail city.

Video obtained by CNN showed Haniyeh’s wife, Umm al-Abed, crying over the coffin and mourning her husband. “You strengthened us every day, making us as strong and determined as iron. We owe it all to you,” she said.

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.

Hezbollah’s leader Hassan Nasrallah said Thursday that Israel’s killing of its top commander had “crossed red lines” and would be met with an “inevitable” response, hinting at coordination with other regional groups.

Nasrallah delivered his speech remotely from a large screen in front of a crowd of mourners attending the funeral of Shukr, the highest-ranking Hezbollah commander to be killed by Israel since Mustafa Badreddine in 2016.

Nasrallah said Israel’s strike in southern Beirut had prompted a “new phase” in the low-intensity battles between Israel and Iran-backed forces in the region.

Iran-backed allies in the region include Iraqi proxy militias, the Houthis in Yemen and groups in Syria.

‘IDF is on high alert’

The chief spokesperson for the Israel Defense Forces (IDF), Rear Admiral Daniel Hagari, said Thursday that Israel was ready to face a range of scenarios amid heightened tension in the region.

“The IDF is on high alert, on both defense and offense. 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 at a briefing Thursday: “We have very good defense systems and in addition we have international partners who have reinforced their forces [deployed] in the region, to help us counter the threats.”

But he cautioned that Israel’s defenses were “not hermetically sealed.”

Hagari noted: “Iran has been running over the past few years a terror infrastructure, to smuggle Iranian explosive devices into Israeli territory to perpetrate attacks. We will continue operating against the Iranian terror with determination.”

Several Israeli agencies and services are stepping up readiness, following the Israeli strike that killed Shukr and threats from Iran that it would retaliate following the assassination of Haniyeh in Tehran.

The emergency services – Magen David Adom (MDA) – said it was prepared for every scenario after a three-day exercise “aimed at preparing for a potential war in the north and blackout scenarios.

MDA said one practised scenario involved a simulated rocket strike on a building in a northern kibbutz in which MDA teams worked with the emergency team from Kibbutz Afek and police.

Israel on Thursday also 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.

The Israeli military said it killed Deif on July 13 in a strike on Khan Younis. Those same attacks also killed at least 90 Palestinians in the sprawling tent city of Al-Mawasi, the Gaza health ministry said. CNN reached out to Hamas to confirm Deif’s death but has not heard back.

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.

CNN’s Mostafa Salem, Tamara Qiblawi, Kareem Khadder, Tamar Michaelis, Tim Lister, Eyad Kourdi, Paul P. Murphy contributed to this report.