Today's attack comes two days before Pope Francis' is scheduled to visit Iraq in a much-anticipated trip that will include Baghdad, southern Iraq and the northern city of Irbil.
The US strike along the border had been in response to a spate of rocket attacks that targeted the American presence, including one that killed a coalition contractor from the Philippines outside Irbil airport.
After that attack, the Pentagon said the strike was a "proportionate military response" taken after consulting coalition partners.
Marotto said the Iraqi security forces were leading an investigation into the attack on Ain al-Asad.
US troops in Iraq significantly decreased their presence in the country last year under the Trump administration. The forces withdrew from several Iraqi based across the country to consolidate chiefly in Ain al-Asad and Baghad.
Frequent rocket attacks targeting the heavily fortified Green Zone, which houses the US Embassy, during President Donald Trump's time in office frustrated the administration, leading to threats of embassy closure and escalatory strikes.