Washington: The United States has bombed the headquarters of the Iran-backed Iraqi Hezbollah militant group in Iraq and Syria, the Pentagon said Sunday, following a rocket attack in Iraq that killed a US civilian contractor.

"In response to repeated Kata'ib Hizbollah (KH) attacks on Iraqi bases that host Operation Inherent Resolve (OIR) coalition forces, US forces have conducted precision defensive strikes against five KH facilities in Iraq and Syria that will degrade KH's ability to conduct future attacks against OIR coalition forces," a Pentagon spokesman said in a statement.

On Friday a barrage of 30 rockets was fired at the K1 Iraqi military base in Kirkuk, an oil-rich region north of Baghdad, a US official told AFP, killing a US civilian contractor.

The United States had accused the group of the 30-plus rocket attack on Friday that killed the U.S. civilian contractor and injured four U.S. service members and two members of the Iraqi Security Forces near the oil-rich city of Kirkuk.

- Inputs from Reuters