The death of Maj. Gen. Qassim Suleimani was reported in Iraqi and Lebanese official media.
Iraqi state television reported Friday that a powerful commander of Iran’s Revolutionary Guards Corps, Maj. Gen. Qassim Suleimani, was killed in a strike on the Baghdad International Airport early Friday.
Iranian and American officials have not confirmed the death of General Suleimani, and it was unclear who carried out the strike.
Iraqi and Lebanese television reported his death, which was confirmed by a senior militia leader in Iraq.
The strikes followed a warning on Thursday afternoon from Defense Secretary Mark T. Esper, who said the United States military would pre-emptively strike Iranian-backed forces in Iraq and Syria if there were signs that the paramilitary groups were planning more attacks against American bases and personnel in the region.
“If we get word of attacks, we will take pre-emptive action as well to protect American forces, protect American lives,” Mr. Esper said. “The game has changed.”
If the reports prove true, the killing of General Suleimani would be a major blow for Iran.
American officials consider General Suleimani, the commander of the Revolutionary Guards’ elite Quds Force, responsible for the deaths of hundreds of American soldiers during the Iraq War and hostile Iranian activities throughout the Middle East.
“If true, this is devastating for the Iranian Revolutionary Guards Corps, the regime and Khamenei’s regional ambitions,” said Mark Dubowitz, chief executive of the hawkish Foundation for Defense of Democracies, a conservative think tank that supports a hard line against Iran, referring to the country’s supreme leader, Ayatollah Ali Khamenei.
“For 23 years, he has been the equivalent of the J.S.O.C. commander, the C.I.A. director and Iran’s real foreign minister,” Mr. Dubowitz said, using an acronym for the United States Joint Special Operations Command. “He is irreplaceable and indispensable” to Iran’s military establishment.
The strike killed five people, including the pro-Iranian chief of an umbrella group for Iraqi militias, Iraqi television reported and militia officials confirmed. The militia chief, Abu Mahdi al-Muhandis, was a strongly pro-Iranian figure.
The public relations chief for the umbrella group, the Popular Mobilization Forces in Iraq, Mohammed Ridha Jabri, was killed as well.
Two other people were killed in the strike, according to an officer at the Baghdad joint command.
The attack appears to have been an airstrike that hit two vehicles, the officer said.
According to a general with the Iraqi Joint Command, General Suleimani and Mr. Ridha, the militia public relations official, arrived by plane at Baghdad International Airport from Syria.
Two cars stopped at the bottom of the airplane steps and picked them up. Mr. al-Muhandis was in one of the cars.
As the two cars left the airport, they were bombed, the general said, speaking on condition of anonymity because he was not authorized to speak to reporters.
The strike was the second attack at the airport within hours.
An earlier attack, late Thursday, involved three rockets that did not appear to have caused any injuries.
The strikes come days after American forces bombed three outposts of Kataib Hezbollah, an Iranian-supported militia in Iraq and Syria, in retaliation for the death of an American contractor in a rocket attack last week near the Iraqi city of Kirkuk.
The United States said that Kataib Hezbollah fired 31 rockets into a base in Kirkuk Province, last week, killing an American contractor and wounding several American and Iraqi servicemen.
The Americans responded by bombing three sites of the Khataib Hezbollah militia near Qaim in western Iraq and two sites in Syria. Khataib Hezbollah denied involvement in the attack in Kirkuk.
Pro-Iranian militia members then marched on the American Embassy on Tuesday, effectively imprisoning its diplomats inside for more than 24 hours while thousands of militia members thronged outside. They burned the embassy’s reception area, planted militia flags on its roof and scrawled graffiti on its walls.
They withdrew late Wednesday afternoon.
President Trump said on Tuesday that Iran would “be held fully responsible” for the attack on the embassy, in which protesters set fire to a reception building on the embassy compound, which covers more than 100 acres. He also blamed Tehran for directing the unrest.
Washington and Tehran appear intent on ratcheting up both their messaging and their forces, raising concerns of a larger conflict. In the past several months, Iranian-supported militias have increased rocket attacks on bases housing American troops. The Pentagon has dispatched more than 14,000 troops to the region since May.
Caught in the middle is the Iraqi government, which is too weak to establish any military authority over some of the more established Iranian-supported Shiite militias.
On Thursday, Mr. Esper said the Iraqi government was not doing enough to contain them. The Iraqis need to “stop these attacks from happening and get the Iranian influence out of the government,” Mr. Esper said.
General Suleimani has long been a figure of intense interest to people in and out of Iran.
He was not only in charge of Iranian intelligence gathering and covert military operations, he was regarded as one of Iran’s most cunning and autonomous military figures. He was also believed to be very close to the country’s supreme leader, Mr. Khamenei, and seen as a potential future leader of Iran.
His presence in Iraq would not have been surprising.
General Suleimani led the Islamic Revolutionary Guards Corps’ Quds Force, a special forces unit responsible for Iranian operations outside Iran’s borders. He once described himself to a senior Iraqi intelligence official as the “sole authority for Iranian actions in Iraq,” the official later told American officials in Baghdad.
In his speech denouncing Mr. Trump, he was even less discreet — and openly mocking.
“We are near you, where you can’t even imagine,” he said. “We are ready. We are the man of this arena.”