“Let me be clear: The U.S. will not tolerate attacks against our people, our interests or our allies,” Defense Secretary Mark Esper told reporters at the Pentagon on Thursday. “All options are on the table as we work with our partners to bring the perpetrators to justice and maintain deterrence.”

His briefing came hours before US forces, likely consisting of drones or warplanes, carried out precision airstrikes in Iraq against targets associated with Kataib Hezbollah, a pro-Iranian paramilitary that is part of Iraq’s Popular Mobilization Forces. The strike was Washington’s response to an attack on Wednesday evening that had killed three personnel at Camp Taji, an Iraqi base where anti-ISIS Coalition forces are stationed. Two Americans and one British service member were killed.

The rocket attack at Camp Taji was the latest in around thirty similar attacks against bases where US forces are located and against US personnel stationed near the US embassy in Baghdad. A similar incident in December led to other airstrikes on Kataib Hezbollah. This is part of the ratcheting up of tensions with Iran that has taken place over the last years and has grown since May 2019.

Iran has carried out mining attacks in the Gulf of Oman, a drone attack on Saudi Arabia, shipped weapons to Houthi rebels in Yemen which the US has intercepted, and fired ballistic missiles at a US base in Iraq. The US killed Iran’s IRGC Quds Force commander Qasem Soleimani in January alongside Kataib Hezbollah leader Abu Mahdi al-Muhandis.

Over the twenty-four hours after the Taji attack the US built a case for another round of airstrikes. It now appears that after the Taji attack there were airstrikes against Iranian-backed forces in Syria near Albukamal on Wednesday evening or Thursday morning just after midnight. But those attacks, the US says, were not carried out by Washington. That led to speculation in the region about who did it.

In the morning in Washington on Thursday the Pentagon made the case for US retaliatory airstrikes against the Iranian-backed groups in Iraq. To make such a case a full-court press was employed from the Secretary of State on down.  Joint Chiefs Chairman Gen. Mark Milley said the attack, which also wounded 14 others, was carried out by “Shia militia groups.” He did not name the group responsible, noting “we have pretty good confidence we know who did this.”

Central Command (CENTCOM) head Gen. Frank McKenzie told US Senators, also on Thursday, that Iran-backed Kataib Hezbollah is the only Shia militia group known to have conducted “an indirect fire attack on this scale against US coalition forces in Iraq.” He referenced back to the December attack when the same group attacked a military base in Kirkuk, Iraq, killing a US contractor.

In response the US had carried out attacks on five positions of Kataib Hezbollah in December, at three sites in Iraq and two in Syria. The group would be help accountable for this week’s attack also. Senators asked about air defense, which the US has said was on the way to Iraq this week. “On that base with these type of rockets, no they were not intercepted. It’s not a function of failure.

There’s not a system there to defend against those types of rockets,” he said. Even though the US has acquired two batteries of Iron Dome, it does not have them deployed and it is unclear if the US has another system to defend against 107mm rockets. The Patriot system is designed for higher altitude threats and defense.

A former administration official told Politico on Thursday that the Wednesday attack was conducted with the “knowledge and support of the IRGC…Although some stated they believed the killing of [Iranian Gen. Qassem] Solemani would prevent further attacks, many more believed it would not and that this is the start of their response,” the former official said.

Asked about the attack, US President Donald Trump said “you will see,” a cryptic response that indicated the wrath of America was only a matter of time. CENTCOM was already preparing the measures necessary and laying out its case. On Thursday it tweeted an array of evidence for other Iranian attacks.

The US airstrikes which followed were described as “defensive” and included precision attacks on five weapon storage facilities of Kataib Hezbollah. “These weapons storage facilities include facilities that housed weapons used to target US and coalition troops.” The US said the attack was proportional.