On December 29, US airstrikes struck the Iran-backed Kataib Hezbollah group in five locations, three in Iraq and two in Syria, in retaliation for a rocket attack against US troops in the K1 military base in Kirkuk two days earlier that killed one American civilian contractor and wounded US and Iraqi troops.
The Kirkuk attack was the latest in a series of rocket attacks targeting US personnel in Iraq in recent weeks but the first to result in casualties. According to The Wall Street Journal, that attack was the 11th time in a mere two months that American troops in Iraq were targeted by rocket fire.
The retaliatory US strikes in western Iraq killed an estimated 25 fighters and wounded 55 more, including four Kataib Hezbollah commanders.
The US described the attacks as "precision defensive airstrikes" and said the targets struck included command and control centres and weapon storage facilities used by the group for organizing attacks against its forces.
These airstrikes were significant given the fact they are the first time the US deliberately targeted and killed fighters belonging to Iraq's state-sanctioned Shiite-majority Hashd al-Shaabi paramilitary.
Before the Kirkuk attack, Washington had warned Tehran that it might take such action.
"Iran should not mistake the United States' restraint for an unwillingness to respond with decisive military force should our forces or interests be attacked," US Defense Secretary Mark Esper warned Tehran earlier this month.
In response to the US airstrikes, Kataib Hezbollah and other Iran-backed Hashd groups might try to launch successive attacks while simultaneously urging the Iraqi parliament to expel all US personnel from the country.
Militarily, it's presently unclear how or if Iran will organize a response.
Israel has bombed several Iranian-backed Shiite militias in Syria in recent years, including Iraqi Hashd fighters, and killed Iranian personnel in the process. Tehran, on numerous occasions, threatened serious retaliation but has to date proven either unable or unwilling to mount any substantial retaliatory attacks against Israel.
In Iraq, Iran-backed groups such as Kataib Hezbollah are suspected of building-up arsenals of artillery rockets, and possibly even short-range ballistic missiles, supplied by Tehran. Consequently, more devastating rocket attacks against US targets in Iraq by such groups could ensue if the situation escalates in the coming weeks and months.
"I would think that the pro-Iran Hashd would want to retaliate quickly," Joel Wing, author of the Musings on Iraq blog, told Rudaw English. "More rocket and mortar attacks on bases with US forces will probably happen."
"On the day of the missile strikes there were calls for US forces to withdraw," he said, adding that such calls have been "going on for months."
Michael Knights, the Lafer Fellow at The Washington Institute for Near East Policy and a noted Iraq expert, predicted that there "may be some retaliation by militias but perhaps not immediately - the militias may try to politically milk the issue and get US forces removed from Iraq through legal means."
"If the Iraqi political and religious class decide to evict US forces, resulting in the collapse of the multi billion dollar annual coalition support by the majority of the G-20 states, then there is nothing for the US to lose in the Iraqi government any more," Knights told Rudaw English.
Wing ultimately doubts that this incident will lead to a major push in Baghdad to have the American military presence in Iraq removed.
"With the government in limbo with the resignation of Prime Minister Adil Abdul Mahdi and no replacement a big move like forcing the Americans out is unlikely to happen," he said.
In the "immediate future" Wing anticipates that the US "is unlikely to take any actions outside of their bases" and that "the diplomatic staff will likely be reduced to avoid any other casualties."
"Other things like training Iraqi forces can continue because that takes place within military camps," he said.
There is very considerable opposition in Iraq to the US troop presence on its soil.
Assaib Ahl al-Haq, another pro-Iran paramilitary in Iraq, released a statement shortly after the US strikes in which it called the American military presence "a burden for the Iraqi state and a source of threat against our forces."
"It is therefore imperative for all of us to do everything to expel them by all legitimate means," the statement added.
Iraqi Prime Minister Abdul Mahdi also said the US strikes violated Iraq's sovereignty and constituted a "dangerous escalation that threatens the security of Iraq and the region."
Powerful Hashd leaders and political figures in Iraq with close ties to Iran were pushing for the removal of US forces from Iraq a year ago when US President Donald Trump visited American troops in Al-Asad airbase in Anbar province without meeting Iraqi officials or even informing them of his visit beforehand.
This was seen by as a grave insult in Iraq with some even charging that it violated the country's sovereignty. Shortly after that, as if adding insult to injury, Trump talked about using Al-Asad as a base to "watch Iran". There were credible fears that another similar affront to Baghdad could have resulted in the Iraqi parliament voting to expel US troops from the country.
Last summer, after Israel was suspected of carrying out airstrikes against Hashd targets in Iraq, Baghdad temporarily closed its airspace and applied new restrictions on US-led anti-ISIS coalition airstrikes in the country.
Under these restrictions, the US and other coalition members require prior approval from Baghdad before carrying out military flights and operations in Iraq's airspace. This predictably "hurt" the anti-ISIS campaign by "reducing the ability of the coalition to use ISR [intelligence, surveillance and reconnaissance] assets to observe and monitor ISIS activity."
Now that the US has targeted Hashd directly, Baghdad might push for more restrictions like these and possibly close Iraqi airspace to the coalition once again. This could have even more adverse effects on the ongoing anti-ISIS campaign, particularly in regions such as Kirkuk where the group retains an active presence in mountainous areas which Baghdad has little to no control over.
Knights pointed that it's likely that the US strikes "were carried out by forces not based in Iraq and not part of Operation Inherent Resolve, so there is no violation of the rules regarding US forces based in Iraq."
He's sceptical that any increased tensions between the US and groups like Kataib Hezbollah in Iraq could seriously undermine the coalition's anti-ISIS operations, arguing that this has essentially happened already.
"The Iran backed militias like Kataib Hezbollah already greatly reduce the amount of assistance the Coalition can provide in the anti-ISIS fight by restricting US ground movement, closing airspace to Coalition aircraft and distracting coalition forces with rocket attacks on their bases," he said.
"So the disruption has already been going on for months."
