The US struck facilities in eastern Syria used by Iran’s Islamic Revolutionary Guard Corps and affiliated groups on Sunday, with a person familiar saying there were likely casualties — a development that could potentially escalate tensions with Tehran.

The strikes were carried out against a training facility and safe house near the cities of Abu Kamal and Mayadin as part of an operation to “disrupt and degrade” the capabilities of Iran-backed forces, according to a US defense spokesperson. The spokesperson said that Iran-affiliated forces were present at the time of the strike but the number of casualties is unclear.

The person familiar with the situation, who asked not to be identified, didn’t have anymore details.

President Joe Biden “directed today’s action to make clear that the United States will defend itself, its personnel, and its interests,” Secretary of Defense Lloyd Austin, who is currently in South Korea, said in an earlier statement released on Sunday in the US.

Tensions between the US and Iran have been climbing since the Oct. 7 Hamas attack on Israel. Iranian officials have warned that new fronts would open against the US if it keeps up unequivocal support for Israel.

Read more: US Launches New Airstrikes on Syria Facility Linked to Iran

The Biden administration has sent military forces to the region, including aircraft carriers, additional fighter jets and troops as part of a broad effort aimed at making Iran and other actors think twice before escalating the war further. The risk is the US presence will only spur the outcome that US officials want to avoid.

US troops have faced at least 41 attacks in Iraq and Syria since Oct. 17 and defense officials say at least 46 military personnel have been injured, some with traumatic brain injuries.

(Updates throughout)