Iraq's top government officials met with leading members of the Hashed al-Shaabi on Monday after a purported Israeli strike on the paramilitary force that risks throwing the country into a proxy war.
Sunday's attack struck a position held by Brigade 45, a Hashed al-Shaabi unit based near Iraq's desertic western border with Syria, killing one fighter and severely wounding a second.
A string of suspicious incidents at Hashed bases over the last month have sparked concern of a possible confrontation between Iran, the US, and Israel on Iraqi soil -- or in its airspace.
On Monday, Iraq's president Barham Saleh hosted the prime minister, speaker of parliament and Hashed top brass to discuss the instability.
"These attacks are a blatant, hostile act that target Iraq," the presidency said in a statement, adding: "Iraqi sovereignty and the wellbeing of its people are a red line."
It stressed the government would take all necessary steps to "deter aggressors and defend Iraq", but did not threaten a military response.
Among the attendees were Hashed chief and national security advisor Faleh Fayyadh, the head of the powerful Badr Corps Hadi al-Ameri and the premier's chief of staff Mohammed al-Hashimi.
On Monday evening, the Hashed said it spotted another drone flying over one of its bases in the northern province of Nineveh.
"It was immediately dealt with using anti-aircraft weaponry. The drone left the area," the group said in a statement.
The incident is the seventh in a barrage of blasts and drone sightings at Hashed bases across Iraq since mid-July, for which no one has claimed responsibility.
The Iraqi government has investigated some of the incidents, blaming an unidentified drone for one and saying another was a "premeditated" act without accusing any side or publishing the probes' full results.
Iraq's military spokesman Yehya Rasool told AFP on Monday the government had launched a new investigation into Sunday's attack.
Asked what diplomatic action Iraq could take, the foreign ministry told AFP it would wait for official conclusions before resorting to the United Nations.
"If it was proven that a foreign entity was involved in these operations, we will take all steps -- first among them, going to the Security Council and the United Nations," spokesman Ahmad Sahhaf said Monday.
The Hashed has already blamed the US and Israel for the spate of attacks, with deputy chief Abu Mehdi al-Muhandis unequivocally pointing the finger at Washington last week.
Sunday's attack was the first time the Hashed directly accused Israel, saying two Israeli drones targeted the Brigade 45 position near Al-Qaim with US air cover.
The attack killed Kazem Mohsen, Brigade 45's "logistical support chief" who was mourned at a funeral procession in Baghdad on Monday.
At the memorial, Ahmad al-Assadi, a lawmaker and spokesman for the Hashed's parliamentary bloc "Fatah", said parliament could hold an emergency meeting to discuss the issue in the coming days.
Fatah had earlier condemned the attack, calling it "a declaration of war on Iraq, its people and its national sovereignty."
The Hashed was established in 2014 from disparate armed groups and volunteers to fight the Islamic State group, which had swept through a third of Iraqi territory.
It operates officially under Iraq's armed forces, but the US and Israel fear some units are an extension of their arch-foe Iran.
The US has been implementing a "maximum pressure" campaign against Iran since withdrawing from the landmark nuclear deal last year.
That has squeezed Baghdad, which has sought to balance between its political ally Washington and its eastern neighbour Tehran.
A government source told AFP that attacks against the Hashed put Baghdad in an ever more difficult position.
"If we stay quiet, we will be seen as weak. If we speak up, some elements of the Hashed will interpret it as a green light to start a war," the source said.
The Pentagon has denied involvement in the attacks, but Israel has neither confirmed nor denied.
Among Israel's top fears is that Iran could transfer missiles to allies in Iraq, Syria and Lebanon.
It has admitted conducting several hundred bombing raids against Iranian forces and their allies in war-torn Syria, including this weekend near Damascus to prevent an alleged drone attack.
But it also stands accused of expanding its bombing campaign to Lebanon, where Hezbollah said a pair of drones targeted the Shiite movement's Beirut stronghold early Sunday.
And on Monday, a pro-Syrian Palestinian group accused Israel of carrying out a drone attack on one of its positions in east Lebanon.