Iraqi and United Nations officials scrambled Thursday to contain the fallout from an unprecedented rocket attack that killed three US-led coalition members and threatened yet another escalation of Iran-US tensions.
Within hours of the attack on the Taji air base north of Baghdad -- the deadliest in years on a base used by US forces in Iraq -- an air strike killed more than two dozen Iran-aligned fighters in neighbouring Syria.
It marked a dramatic uptick in violence less than three months after rockets killed a US contractor in northern Iraq, unleashing a round of tit-for-tat attacks between Washington and Tehran on Iraqi soil.
Fearing an even bloodier flare-up this time, Iraqi officials and the United Nations were quick to condemn the deaths.
Iraq's military command said it was "a serious security challenge" and pledged to open an investigation.
President Barham Saleh and parliament speaker Mohammed al-Halbussi condemned a "terrorist attack" which targeted "Iraq and its security."
The UN mission in Iraq called for "maximum restraint on all sides".
"These ongoing attacks are a clear and substantial threat to the country, and the risk of rogue action by armed groups remains a constant concern," it said.
"The last thing Iraq needs is to serve as an arena for vendettas and external battles."
Briton, Americans killed
Wednesday's attack was the 22nd on US interests in Iraq since late October.
It saw a volley of 18 rockets slam into the Taji air base, one of about a dozen facilities across Iraq where coalition forces are based.
The coalition confirmed three of its personnel were killed and around a dozen more wounded.
One of the dead was a member of the Royal Army Medical Corps, Britain confirmed. A US military official told AFP the other two were a US soldier and an American contractor.
There was no immediate word on Iraqi casualties.
No group claimed responsibility, but Washington has accused hardline factions of Iraq's Hashed al-Shaabi paramilitary alliance of carrying out similar attacks.
The Hashed is a web of mostly Shiite armed factions, many of which have close ties with neighbouring Iran, and has been incorporated into the Iraqi military.
In late December, the US accused Iran-aligned faction Kataeb Hezbollah of killing an American contractor at a base in northern Iraq.
It responded with air strikes in western Iraq that killed 25 of the group's fighters.
Days later, a US drone killed senior Iranian commander Qasem Soleimani and Hashed deputy chief Abu Mahdi al-Muhandis near Baghdad airport.
Iran then launched its own strikes on a western Iraqi base, leaving dozens of US troops suffering from brain trauma.
Hashed factions have repeatedly pledged to avenge Muhandis's death in their own way.
Hashed hammered in Syria
Within hours of Wednesday's attack, an air strike killed 26 Iran-aligned Iraqi fighters in neighbouring Syria, the Syrian Observatory for Human Rights said.
The Britain-based war monitor said it was carried out by three planes which probably belonged to the US-led coalition.
Iraq counts years of close ties with both Iran and the United States, and has been put in an increasingly difficult position by the spiralling tensions between its allies.
In January, Iraqi lawmakers voted to oust all foreign troops from Iraq in reaction to the killing of Soleimani and Muhandis.
Some 5,200 US troops are stationed in Iraq as part of the coalition formed in 2014 to fight the Islamic State jihadist group.
While IS has lost all of the territory it once held in Iraq and Syria, sleeper cells remain capable of carrying out attacks on both sides of the border.
On Sunday, two US soldiers were killed north of Baghdad while helping Iraqi forces battle IS remnants.
US officials previously told AFP they considered the Hashed a bigger threat than IS, given the frequency and accuracy of rocket attacks on US troops that could be traced back to the paramilitaries.