Iran vowed Friday to avenge Israel’s killing of senior commanders and other officers of its elite Quds Force, at a public funeral held for the dead men, elevating fears of open war but leaving unsaid how it would retaliate or when.

“Our brave men will punish the Zionist regime,” Gen. Hossein Salami, the commander in chief of Iran’s Revolutionary Guard, told the crowd attending the funeral in Tehran, Iran. “We warn that no act by any enemy against our holy system will go unanswered, and the art of the Iranian nation is to break the power of empires.”

On Monday, Israel conducted an airstrike on a building that is part of the Iranian Embassy complex in Damascus, Syria, killing three generals and four other officers of the Quds Force. The force, an arm of the Revolutionary Guard, conducts military and intelligence operations outside Iran, often working closely with allies that oppose Israel and the United States, including Syria, Hezbollah in Lebanon and Hamas.

Hassan Nasrallah, the leader of Hezbollah, delivered a video speech that was broadcast in Iran and in Lebanon during the funeral, saying that a response from Iran could come anytime and that “we must be prepared for all eventualities.”

“Be certain that the Iranian response to the targeting in Damascus is inevitably coming,” Nasrallah said.

U.S. officials in Washington and the Middle East said Friday that they were bracing for possible Iranian retaliatory strikes. U.S. military forces in the region have been placed on heightened alert. Israel has also placed its military on high alert, according to an Israeli official, canceled leave for combat units, recalled some reservists to air defense units and blocked GPS signals.

Four years ago, after the United States killed the chief of the Quds Force, Maj. Gen. Qassem Soleimani, Iran fired missiles at U.S. bases in Iraq, injuring more than 100 troops.

Iran’s ambassador to the United Nations, Amir Saeid Iravani, said Thursday that he would sit down for interviews with U.S. media “after Iran’s response to Israel.”

Although its proxy militias around the Middle East have launched a number of attacks on Israel since the war between Israel and Hamas began Oct. 7, Iran has taken care to avoid a direct conflict that could lead to full-fledged war.

Two Iranian officials who asked not to be named because they were not authorized to speak publicly said Iran had placed all its armed forces on full high alert and a decision had been made that Iran must respond directly this time to create deterrence.

In the past few months, Israel has killed at least 18 members of the Quds Force, among them four senior commanders who were veterans of Middle East wars, according to Iranian media. But the airstrike in Damascus was far out of the ordinary, both in killing so many senior figures at once, and in hitting a diplomatic building, normally considered off-limits in conflicts. Israeli officials said the building functioned as a Revolutionary Guard base, and so was a legitimate target.

The building housed the official residence of Iran’s ambassador to Syria, who said on state television that he and his family had left the building when it was hit.

The final decision on a matter as important as a strike against Israel rests with Supreme Leader Ayatollah Ali Khamenei, who is also the commander in chief of the armed forces. It was Khamenei who ordered the 2020 attack in retaliation for the killing of Soleimani.

U.S. military analysts assess that it is more likely that Iran would strike Israel itself rather than have its proxies attack U.S. troops in the region, including in Iraq and Syria, as they did more than 170 times in the four months after the Hamas-led Oct. 7 assault against Israel. Those attacks against American targets stopped in early February, but Pentagon officials said they were watching the situation closely.

An Israeli defense official said that Israeli analysts had reached the same conclusion, that Iran itself would attack and not act through Hezbollah, its closest militant ally, which has been engaging in regular exchanges of fire with Israeli forces since the war began.

Prime Minister Benjamin Netanyahu of Israel, before a security Cabinet meeting about a potential Iranian attack, said Thursday, “We will know how to defend ourselves and we will act according to the simple principle of whoever harms us or plans to harm us — we will harm them.”