Shortly before the United States and Israel were poised to launch an attack on Iran, the C.I.A. zeroed in on the location of perhaps the most important target: Ayatollah Ali Khamenei, the country’s supreme leader.

The C.I.A. had been tracking Ayatollah Khamenei for months, gaining more confidence about his locations and his patterns, according to people familiar with the operation. Then the agency learned that a meeting of top Iranian officials would take place on Saturday morning at a leadership compound in the heart of Tehran. Most critically, the C.I.A. learned that the supreme leader would be at the site.

The United States and Israel decided to adjust the timing of their attack, in part to take advantage of the new intelligence, according to officials with knowledge of the decisions.

The information provided a window of opportunity for the two countries to achieve a critical and early victory: the elimination of top Iranian officials and the killing of Ayatollah Khamenei.

The remarkably swift removal of Iran’s supreme leader reflected the close coordination and intelligence sharing between the United States and Israel in the run-up to the attack, and the deep intelligence the countries had developed on Iranian leadership, especially in the wake of last year’s 12-day war. The operation also showed the failure of Iran’s leaders to take adequate precautions to avoid exposing themselves at a time where both Israel and the United States sent clear signals that they were preparing for war.

The C.I.A. passed its intelligence, which offered “high fidelity” on Ayatollah Khamenei’s position, to Israel, according to people briefed on the intelligence.

They and others who shared details about the operation spoke on the condition of anonymity to discuss sensitive intelligence and military planning.

Israel, using U.S. intelligence and its own, would execute an operation it had been planning for months: the targeted killing of Iran’s senior leaders.

The United States and Israeli governments, which had originally planned to launch a strike at night under the cover of darkness, made the decision to adjust the timing to take advantage of the information about the gathering at the government compound in Tehran on Saturday morning.

The leaders were set to meet where the offices of the Iranian presidency, the supreme leader and Iran’s National Security Council are located.

Israel had determined that the gathering would include top Iranian defense officials, including Mohammad Pakpour, the commander in chief of the Islamic Revolutionary Guards Corps; Aziz Nasirzadeh, the minister of defense; Adm. Ali Shamkhani, the head of the Military Council; Seyyed Majid Mousavi, the commander of the Islamic Revolutionary Guards Corps Aerospace Force; Mohammad Shirazi, the deputy intelligence minister; and others.

The operation began around 6 a.m. in Israel, as fighter jets took off from their bases. The strike required relatively few aircraft, but they were armed with long-range and highly accurate munitions.

Two hours and five minutes after the jets took off, at around 9:40 a.m. in Tehran, the long-range missiles struck the compound. At the time of the strike, senior Iranian national security officials were in one building at the compound. Ayatollah Khamenei was in another nearby building.

“This morning’s strike was carried out simultaneously at several locations in Tehran, in one of which senior figures of Iran’s political-security echelon had gathered,” an Israeli defense official wrote in a message reviewed by The New York Times.

The official said that despite Iranian preparations for war, Israel managed to achieve “tactical surprise” with its attack on the compound.

The White House and the C.I.A. declined to comment.

On Sunday, Iran’s state news agency, IRNA, confirmed the deaths of two high-level military leaders whom Israel said it had killed on Saturday: Admiral Shamkhani and General Pakpour.