A nearly week-long barrage of anonymous shelling attacks on American interests across Iraq are intended to signal Iran's long reach and "embarrass" Baghdad amid spiralling US-Iran tensions, observers say.
The incidents were not claimed but largely originated from areas where Shiite-dominated armed groups loyal to Tehran and deeply opposed to Washington have free reign.
Starting Friday, mortars and rockets have rained down on the Al-Balad and Taji bases, the Baghdad military airport, and a military command centre in northern Mosul -- all sites where US troops and army equipment are present.
Responding to the attacks, Iraqi premier Adel Abdel Mahdi said Tuesday evening it was "forbidden" for any Iraqi forces to operate independently of the military.
"We cannot allow this to continue," he told reporters.
But hours later, several rockets slammed into fields in the oil-rich area of Basra, where US companies including ExxonMobil and Baker Hughes are operational.
"This is Iran's way of displaying its leverage through its assets in Iraq," Fanar Haddad, an Iraq expert at the National University of Singapore, told AFP.
"These attacks demonstrate the ability not just to harm US personnel, not just to embarrass and outflank the Iraqi government and America's Iraqi partners -- but to also threaten international energy flows and disrupt the operations of major international oil companies," Haddad said.
- Pressure points -
Iraq has strong military and diplomatic ties to the US, but it is also very close to Tehran -- one of Baghdad's top trade partners with sway over many Shiite armed units.
Since the US withdrew last year from a landmark nuclear deal with Iran and reimposed tough sanctions on the Islamic republic, Iraq has had to walk a fine line to maintain good ties with both.
Abdel Mahdi has repeatedly offered to mediate between his two allies and has appealed to the US for "calm".
But day by day the tensions seem more likely to sweep up Iraq, which had been enjoying a period of relative calm after decades of conflict, most recently against the Islamic State group.
One point of contention has been America's troop presence, which peaked at some 170,000 more than a decade ago but has since dropped to around 5,200 US soldiers stationed across the country alongside Iraqi forces.
Iraq has pledged to protect foreign troops and commercial interests on its territory from unlawful attacks, making the recent attacks "another embarrassment", according to security expert Hisham al-Hashemi.
"They foiled the government's narrative on the relative stability and its invitations to big firms to invest in Iraq," he said.
A government source told AFP that officials felt "under pressure".
"The areas where US and other foreign military advisors are based are being regularly bombed, and this is an embarrassment," the official said.
On Wednesday, Iraq's military said it was doubling its efforts to find those behind the attacks, but a military source told AFP not to expect much from the investigation.
"Security forces are intensifying their efforts to prevent such terrorist attacks, but the problem is that those behind them can easily reach these areas," the source said.
- Expats evacuate -
Another vulnerable target could be Iraq's oil sector, which provides virtually all of the government's revenues.
Iraq is the second-largest oil producer among the Organization of the Petroleum Exporting Countries (OPEC) and exports around 3.5 million barrels per day.
A vast majority of that crude is exported from Basra through the Strait of Hormuz, a key waterway where a third of the world's seaborne oil is shipped and which Iran has threatened to shut in case of a conflict with the US.
That would leave Baghdad "totally strangled", according to Ruba Husari, an expert in Iraq's oil industry.
"The Gulf waterways are its lifeline and a restricted access to the Mideast Gulf will hurt it badly," she said.
Oil ministry spokesman Assem Jihad has told AFP that no other port could export the same amounts as Basra in case the Gulf channel was shut, but said production and exports have not been affected.
An industry source at the Rumailah field said Wednesday that US companies at the field, including ExxonMobil and General Electric's Baker Hughes, had ordered senior expatriate employees out.
"There's a red alert issued by the American companies. The senior expat management are leaving today and tomorrow," the source told AFP, saying it was the same level of alert issued in May.
ExxonMobil withdrew its 83 expatriate workers from a nearby oil field in mid-May, but they returned after "guarantees" from the government.
But Iraq is not in the clear yet, said Haddad.
"The bullish stance adopted by all sides and the absence of meaningful dialogue magnify the possibilities for escalation," he told AFP.
"The risks of a major conflict have seldom been higher."