The U.S. military retaliated for attacks on U.S. troops in Iraq.
It launched airstrikes against what it says were "facilities used by Iran-backed militia groups."
The strikes hit targets near the border between Syria and Iraq.
A Pentagon official says the militia groups were using the sites to launch attacks against U.S. troops. He called it a defensive attack.
Iraqi officials said that at least four militia members were killed. A human rights group there reported at least five deaths.