President Biden on Sunday ordered precision airstrikes against facilities used by Iran-backed militia groups in the Iraq-Syria border region, the U.S. Department of Defense said in a statement.

The targets were facilities that Iran-backed militias were using to engage in drone attacks against U.S. personnel and facilities in Iraq, the DOD said. They targeted operational and weapons storage facilities at two spots in Syria and one in Iraq, all near the border of both countries.

“As demonstrated by this evening’s strikes, President Biden has been clear that he will act to protect U.S. personnel,” the DOD said. “Given the ongoing series of attacks by Iran-backed groups targeting U.S. interests in Iraq, the President directed further military action to disrupt and deter such attacks. We are in Iraq at the invitation of the Government of Iraq for the sole purpose of assisting the Iraqi Security Forces in their efforts to defeat ISIS. The United States took necessary, appropriate, and deliberate action designed to limit the risk of escalation - but also to send a clear and unambiguous deterrent message.”

The strikes were retaliation for drone attacks, the Pentagon said.

Similar retaliatory attacks had been ordered in February, USA Today noted, in response to rocket attacks on a northern Iraq base in which a contractor was killed and troops were wounded. The sites struck over the weekend were the source of drone attacks against U.S. installations, the Pentagon said.

“Specifically, the U.S. strikes targeted operational and weapons storage facilities at two locations in Syria and one location in Iraq, both of which lie close to the border between those countries,” Pentagon press secretary John Kirby said in a statement. “Several Iran-backed militia groups, including Kata’ib Hezbollah and Kata’ib Sayyid al-Shuhada, used these facilities.”