Speaking on condition of anonymity, a senior Iraqi official from South Oil Company said oil flows out of the country's key southern pipelines ceased late on Sunday.
The official said exports were not likely to resume for at least a week.
"Oil exports from the port of Basra have completely stopped since last night," he said.
The country's southern pipelines export 90% of Iraq's oil.
Exports out of the south normally average about 1.85 million barrels per day (bpd).
A stop in southern oil exports cost Iraq about $60 million a day in lost income at current global crude prices, said Walid Khadduri, an oil expert who is chief editor of the Cyprus-based Middle East Economic Survey.
On Sunday, saboteurs blew up a cluster of pipelines in southern Iraq in what was the latest attack targeting the country's crucial oil industry, officials said.
The strikes against five pipelines linked to the Rumeila oilfields immediately shut down the Zubair 1 pumping station, forcing officials to use reserves from storage tanks to keep exports flowing for several hours. The reserves ran out late on Sunday.
Before the attack, Iraq's south
exports were 600,000 bpd
The South Oil Company official said before Sunday's attack Iraq's exports from the south were about 600,000 bpd - already a third less than the normal average of 1.8 million bpd due to a separate string of attacks early last week.
The pipelines were still ablaze on Monday, he said.
On Saturday, saboteurs blew up another pipeline in the West Qurna oilfields, about 150km north of Basra.
Resistance fighters have launched repeated attacks on Iraq's oil infrastructure in a bid to undermine the interim government and reconstruction efforts.
Saboteurs last brought southern oil exports to a halt in June.