The US strikes against Iran-backed militia Kataib Hezbollah is part of a series of retaliations that is central to rising tension between Washington and Tehran, experts say.
The attacks on an Iraqi state-sanctioned militia and Iran's calls for retaliation represent a new escalation in the proxy war between Washington and Tehran.
At least 25 people were killed and more than 50 injured in the strikes on five bases controlled by Kataib Hezbollah late on Sunday.
Washington said the strikes were in response to a rocket attack that killed a US civilian contractor at a military compound in northern Iraq on Friday.
Attacks on bases that house US troops have recently increased but have not been claimed by any faction.
But now, Washington is openly increasing its campaign against pro-Iran groups in Iraq, Renad Mansour, director of the Iraq initiative at London's Chatham House, told The National.
“Some would see this as a tit-for-tat following the killing of a US contractor in Kirkuk, creating a base for Iraq to become a battlefield, especially as tensions between the two continue to escalate,” Mr Mansour said.
Washington this year imposed economic sanctions on Tehran through its “"maximum pressure" campaign, and Iran responded with calls for "maximum resistance".
Kataib Hezbollah falls under the Popular Mobilisation Forces, an umbrella group of paramilitary units that was formally integrated into Iraq's armed forces during the fight against ISIS.
Most of the PMF members are backed by Iran.
Kataib Hezbollah has long attacked US forces and was one of the first groups to send fighters to Syria to support President Bashar Al Assad in the civil war.
Washington designated the group a foreign terrorist organisation in 2009, saying it threatened stability in Iraq, one of the most important US allies in the Arab world.
The group's founder, Jamal Ibrahimi, known by his nom de guerre Abu Mahdi Al Muhandis, has warned of a strong response against US forces.
The conflict between the US and Iran has been exposed in Iraq, Jaber Al Jaberi, an MP representing Anbar, told The National.
“This indicates that they have lost hope in the Iraqi government and its ability to control the militias,” he said. “It is a disciplinary warning and blow to the group as their losses were high.”
The US action also makes sure that the response is so painful that an escalation is highly unlikely, said Michael Stephens, a Middle East expert at the Royal United Services Institute.
"Everyone knows the rules: do not kill anyone and there is no problem. I guess the strikes were designed to reinforce that rule," Mr Stephens told The National.
Hisham Al Hashimi, an Iraqi researcher and security adviser to the government, said it appeared that Kataib Hezbollah understood they could no longer carry out operations against US troops in the region.
"They will only threaten via rhetoric and the media because the response will be much more severe if they are to carry out any attacks," Mr Al Hashimi told The National.
