Iran has launched a major ballistic missile attack on US-led forces in Iraq, the US military said on Tuesday, potentially triggering a new round of escalation in the confrontation between the United States and Tehran.

The US military said an assessment was underway to determine damage and any casualties at al-Asad airbase in Iraq, which hosted President Donald Trump in December of 2018, as well as at another facility in Erbil.

In a statement, the US military said Iran launched the attack at about 1:30 am local time, firing more than a dozen ballistic missiles against US-led forces in Iraq.

“It is clear that these missiles were launched from Iran,” Pentagon spokesman Jonathan Hoffman said in statement.

“As we evaluate the situation and our response, we will take all necessary measures to protect and defend US personnel, partners, and allies in the region.”

The attack came just hours after US Defense Secretary Mark Esper said the United States should expect Iran to retaliate over the US killing of Iranian military commander Qassem Soleimani in a drone strike on Friday.

Esper declined to detail any intelligence driving that assessment or comment on Iranian military activities that could signal Tehran’s intentions.

Reuters has reported that Iranian missile forces have been put on a heightened state of alert.