Pentagon chief Lloyd Austin said in an interview Sunday that the United States would “do whatever it takes to defend itself” after rockets were fired at US troops in Iraq.

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Ten rockets hit the Ain al-Assad airbase on Wednesday, killing a U.S. citizen’s deputy contractor. The United States has so far refrained from directly blaming one of Iran’s pro-Iraqi militias for the attack, as many of its predecessors have done in recent weeks.

“We urge Iraqis to act swiftly to investigate this incident, and they are doing so,” Austin told the ABC Channel, adding that his country was still gathering information about its perpetrators.

“But you can expect us to always be responsible for their actions,” he said. “The message for those who carry out such an attack is that we expect to do what is necessary to defend ourselves.”

“If we think we have to do it, when and where we choose to do it, we will strike,” he continued. “We demand the right to protect our troops.”

The channel asked the Pentagon chief if Iran had been notified that retaliation did not mean an increase.

“I think Iran is fully capable of evaluating … the strike and our actions and they will make their own decisions,” Austin replied.

“But what they need to get out of this is that we are going to defend our military. Our response is thoughtful and appropriate. We hope they will do the right thing.”

News of the rocket fire comes amid tensions between Washington and Tehran over Iran’s nuclear program and the prospect of talks resuming the 2015 deal.