Exports through the country's other export outlet in the north have been long interrupted because of sabotage on the pipeline.
A port official and an employee at the South Oil Company, which runs Iraq's southern oilfields, said pumping stopped at 7 am on Monday. Both men spoke on condition of anonymity because they are not authorised to talk to the media.
They gave no further details. But an official with a shipping company in Dubai confirmed that exports from southern Iraq had ceased because of the power cut.
"Oil terminals have completely stopped exports from Basra and Khor al-Amaya," said Mohammed Hadi, head of Iraq Operation for Norton Lilly International. "Both terminals use the same power source."
Electricity was cut through Baghdad and many parts of Iraq early on Monday after an attack on a major electricity feeder line between Beiji and the capital.
"Oil terminals have completely stopped exports from Basra and Khor al-Amaya"
Iraq Operation, Norton Lilly International
Government spokesman Laith Kubba said on Sunday that the attack occurred two days ago, "and this will, of course, affect the power supply in Baghdad".
He said repairs were under way. Iraq exports about 1.5 million barrels a day from the south. Exports from the northern oilfields around Kirkuk have long been interrupted because of sabotage on the pipelines.
Officials at the Northern Oil Company, which runs the northern fields, said that every three or four months there was some limited pumping of about 250,000 barrels to the Ceyhan port in Turkey.
But no shipments are being made to Ceyhan, the officials said.