"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.

The targets -- three in Iraq and two in Syria -- included weapons storage facilities and command locations used to plan and execute attacks, the statement added.

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

A direct hit on an ammunition depot caused secondary explosions, and four more rockets were found in their tubes in a truck at the launch point.

Washington had recently promised "a decisive US response" to a growing number of unclaimed attacks on its interests in Iraq, which it blames on pro-Iran factions.

US-Iran tensions have soared since Washington pulled out of a landmark nuclear agreement with Tehran last year and imposed crippling sanctions.

Iraq, meantime, has been gripped by its biggest anti-government street protests since the US-led invasion of 2003 that toppled dictator Saddam Hussein.