Iranian proxy forces launched a missile attack against a U.S. base in Syria on Friday, one day after the U.S. military conducted several airstrikes against Iran-aligned groups in retaliation for an Iranian drone attack killed a U.S. contractor and injured five service members.

The Iranian-aligned groups launched roughly seven rockets on Friday targeting an American base southeast of the Syrian province of Der el-Zour. No known U.S. casualties were recorded in initial assessments.

“We’re going to work to protect our people and our facilities as best we can. It’s a dangerous environment,” White House national security spokesman John Kirby told CNN.