The bomb that killed Ismail Haniyeh, the top leader of Hamas, in Iran early Wednesday was planted several weeks ago, according to a new report.

Haniyeh traveled to Tehran to attend the inauguration ceremony of Iran’s new president, Masoud Pezeshkian, and had been seen at the event in the hours before the attack.

Sources told The New York Times that assassins planted the explosive roughly two months ago in a Tehran guesthouse protected by the Islamic Revolutionary Guards Corps where Haniyeh had stayed before.

Breaking News: Ismail Haniyeh, the Hamas leader assassinated in Iran this week, was killed by a bomb smuggled into his guesthouse months ago, Middle Eastern officials said. https://t.co/O8sfQVjnNE

— The New York Times (@nytimes) August 1, 2024

When it was confirmed that Haniyeh was in his room at the guesthouse, the explosive was detonated remotely early on Wednesday, killing him and a bodyguard, officials said.

Photos showed that the explosion, which resulted in a loud noise, shook the building, shattered windows, and knocked down part of an exterior wall.

The report said a team of medics rushed to the room and declared Haniyeh dead. They tried, unsuccessfully, to revive the bodyguard.

Khalil al-Hayya, the deputy commander of Hamas in the Gaza Strip who was also in Tehran, arrived at the scene and saw Haniyeh’s corpse, officials said.

Sources told the newspaper the room next door, where Palestinian Islamic Jihad leader Ziyad al-Nakhalah was staying, was not badly damaged in the blast.

The report emphasized that it was not clear how the bomb made its way into the guesthouse. It also dismissed early speculation of a missile strike.

Iranian and U.S. officials have pinned the assassination on Israel, which has not publicly claimed responsibility for the attack, according to the report.

However, sources told the newspaper that Israeli intelligence officials briefed U.S. and other Western governments on the operation after it took place.

A top Israeli intelligence official had vowed to “take out” Hamas, including in foreign countries, after the group’s October 7 terrorist attacks.

In retaliation for the killing of Haniyeh this week, Iranian Supreme Leader Ayatollah Ali Khamenei ordered a direct strike on Israel.

Israel Defense Forces said on Thursday that a July 13 strike in Gaza killed Mohammed Deif, the commander of the terrorist group Hamas’ military wing, who was second only to Yahya Sinwar in the strip.