Three Iranian officials informed on the order said that Ayatollah Ali Khamenei, Iran's supreme leader, has ordered Iran to launch a direct assault against Israel in retaliation for the death of Hamas leader Ismail Haniyeh in Tehran.

Shortly after Iran declared that Mr. Haniyeh had died, three Iranian officials—two of whom were Revolutionary Guard members—spoke of Mr. Khamenei's directive during an urgent meeting of the Supreme National Security Council on Wednesday morning. Since they lacked the right to speak in public, they requested that their identities not be revealed.

Israel, which is at war with Hamas in the Gaza Strip, has neither admitted nor denied killing Mr. Haniyeh, who was in Tehran for the coronation of Iran's new president. Iran and Hamas have accused Israel of carrying out the assassination. Israel has a lengthy history of eliminating adversaries abroad, such as military chiefs and nuclear scientists in Iran. Iran's nuclear scientists and military chiefs are among Israel's many foreign foes that it has long killed.

Through almost 10 months of war in Gaza, Iran has tried to strike a balance, putting pressure on Israel with sharply increased attacks by its allies and proxy forces in the region, while avoiding an all-out war between the two nations.

In April, Iran made its biggest and most overt attack on Israel in decades of hostility, launching hundreds of missiles and drones in retaliation for an Israeli strike on its embassy compound that killed several Iranian military commanders in Damascus, Syria. But even that show of force was telegraphed well in advance, nearly all the weapons were shot down by Israel and its allies, and little damage was done.

Now it is unclear how forcefully Iran will respond, and whether it will once again calibrate its attack to steer clear of escalation. Iranian military commanders are considering another combination attack of drones and missiles on military targets in the vicinity of Tel Aviv and Haifa, but would make a point of avoiding strikes on civilian targets, the Iranian officials said. One option under consideration is a coordinated attack from Iran and other fronts where it has allied forces, including Yemen, Syria and Iraq, for maximum effect, they said.

Mr. Khamenei, who has the last word on all state matters and is also the commander in chief of the armed forces, instructed military commanders from the Revolutionary Guards and the army to prepare plans for both an attack and a defense in the event that the war expands and Israel or the United States strike Iran, the officials said.

In his public statement about Mr. Haniyeh’s death, Mr. Khamenei signaled that Iran would retaliate directly, saying, “we see avenging his blood our duty,” because it happened on the territory of the Islamic Republic. He said Israel had set the stage for receiving “a severe punishment.”

Statements from other Iranian officials, including the new president, Masoud Pezeshkian, the foreign ministry, the Guards and Iran’s mission to the U.N., also said openly that Iran would retaliate against Israel and that it had a right to defend itself against a transgression on its sovereignty.

Iran and the regional forces it backs — Hamas, Hezbollah in Lebanon, the Houthis in Yemen and multiple militias in Iraq — form what they call the “axis of resistance.” Leaders of those groups were in Tehran for the inauguration of Mr. Pezeshkian on Tuesday. Mr. Haniyeh was assassinated at about 2 a.m. local time, after attending the ceremony and meeting with Mr. Khamenei.

The killing shocked Iranian officials, who described it as crossing red lines.

It was a humiliating security breach for a country eager to project strength but long frustrated by its inability to prevent Israel from carrying out covert operations on its soil. The embarrassment was compounded by Mr. Haniyeh’s prominence, the presence of other allies, and that he was attacked at a highly secure Revolutionary Guards guesthouse on a day of heightened security in the capital.

Many Iranian supporters of the government and officials expressed outrage at the failure to thwart the assassination, saying only a handful of senior security officials would have known where Mr. Haniyeh was staying. Some took to social media to say that Iran’s first priority should be to clean house and ensure the safety of its senior officials.

“Before revenge first ensure the safety of the supreme leader,” said Alireza Katebi Jahromi, a journalist and supporter of Iran’s government, in a post on X.

Iranian officials don’t view Mr. Haniyeh’s assassination as just Israel’s opportunistic killing of one of its foes, but also as an affront to their security apparatus that suggests anyone in Iran, at any level, could be targeted and killed.

Analysts said that Iran sees retaliation as necessary for both avenging the killing of Mr. Haniyeh but also deterrence against Israel killing other powerful enemies, like Hassan Nasrallah, the leader of Hezbollah, or Gen. Ismail Qaani, the commander of the Quds Forces who oversees the militant groups outside Iran.

“Iran likely believes it has no choice other than retaliating to deter further Israeli attacks, defend its sovereignty, and preserve its credibility in the eyes of its regional partners,” said Ali Vaez, the Iran director of the International Crisis Group.