WASHINGTON — Defense Secretary Mark T. Esper said on Thursday that Iranian-backed militias were behind an attack on a joint U.S.-Iraqi base that killed two American service members and a soldier from Britain.
Speaking to reporters at the Pentagon, Mr. Esper said that “all options are on the table” for retaliatory strikes against the group responsible for the deadly missile attack on Wednesday.
“Let me be clear: The United States will not tolerate attacks against our people, our interests or our allies,” Mr. Esper said.
What comes next remains unclear.
In December, an Iraqi militia with ties to Iran, called Kataib Hezbollah, was accused of a rocket strike that killed an American contractor, setting off a series of events that led the United States to the brink of war with Iran.
Gen. Mark A. Milley, the chairman of the Joint Chiefs of staff, spoke alongside Mr. Esper and said he had “good confidence” who was behind the attack.
Retaliatory options are being presented to the president, officials said.
The two Americans killed Wednesday were with the Army and the Air Force, according to one American official, and more than a dozen members of the American-led military coalition, including those from Poland and civilian contractors, were wounded.
Roughly 30 rockets were fired from a homemade mobile launcher miles outside the base, Camp Taji, and more than a dozen hit the sprawling installation roughly 15 miles north of Baghdad, officials said.
After the rocket attack in December, the United States struck five bases held by Kataib Hezbollah.
Those strikes were followed by a siege of the American Embassy in Baghdad and then a U.S. airstrike that killed the leader of Iran’s elite Quds force, Maj. Gen. Qassim Suleimani, and Abu Mahdi al-Muhandis, a top Iraqi militia leader with ties to Iran.
The rapid pattern of escalation ended weeks later when Iran launched 16 ballistic missiles at bases in Iraq that housed American forces. No one was killed by those strikes, but dozens suffered traumatic brain injuries — some of whom had to be evacuated out of the country.
The American casualties in Taji on Wednesday marked a deadly several days for U.S. forces in Iraq. On Sunday, Capt. Moises A. Navas of Germantown, Md., and Gunnery Sgt. Diego D. Pongo of Simi Valley, Calif., two Marine Raiders, were killed during a vicious gunfight against Islamic State fighters in northern Iraq.
The episode prompted a review of current American operations against the Islamic State, given the intensity of the mission and the fact that the Marines had not planned for such a battle in a sprawling cave complex. Members of the American military’s elite Delta Force were ordered to respond and recover the dead.
According to a Pentagon database, before Wednesday’s attack, 19 Americans had been killed in combat in Iraq and Syria since the start of the campaign against the Islamic State, known as Operation Inherent Resolve.
Eric Schmitt contributed reporting.