A day after the US conducted deadly airstrikes against Iran-backed militia in Iraq and Syria, a US Army base in Syria came under rocket fire on Monday.

The US Army spokesperson confirmed that the US troops responded to the bombardment by firing back in self-defence and managed to escape injury.

In an official statement, Colonel Wayne Marotto said, “There are no (US) injuries and the damage is being assessed.” He did not say who was responsible for the attack on US. troops.

According to sources, an Iranian-backed militia group had fired a few artillery rounds in the vicinity of al Omar oil field, which is controlled by the US-backed Syrian Democratic Forces.

The rocket fire underscored the risk of escalation and the limits of US military firepower to restrain Iran-aligned militias that Washington blames for a series of increasingly sophisticated drone strikes against US personnel and facilities in Iraq.

Following the US-led airstrikes in Iraq and Syria on Sunday, US Secretary of State Antony Blinken and the White House had defended the attack calling it a way to tamp down on the risk of conflict.

“We took necessary, appropriate, deliberate action that is designed to limit the risk of escalation, but also to send a clear and unambiguous deterrent message,” Blinken said.

It was the second time US President Joe Biden had ordered retaliatory strikes against Iran-backed militias since taking office five months ago. He ordered limited strikes in Syria in February, that time in response to rocket attacks in Iraq.

Biden’s administration has been looking to potentially revive a 2015 nuclear deal with Iran. The attacks underscore how Biden aims to compartmentalize such defensive strikes, while simultaneously engaging Tehran in diplomacy.