LONDON- Saudi Arabia has restored more than 75% of crude output lost after attacks on its facilities and will return to full volumes by early next week, a source briefed on the latest developments told Reuters on Monday.

Saudi's oil production from its Khurais plant is now at more than 1.3 million barrels per day, while current production from its Abqaiq plant is at about 3 million bpd, the source said.

The Sept. 14 attacks on the Abqaiq and Khurais plants, some of the kingdom's biggest, caused raging fires and significant damage that halved the crude output of the world's top oil exporter, by shutting down 5.7 million barrels per day of production. 

Saudi Energy Minister Prince Abdulaziz bin Salman and the chief executive of state oil company Aramco, Amin Nasser, have said the output will be fully back online by the end of September. 

The kingdom has managed to recover supplies to customers to the levels they were at prior to the attacks by drawing from its huge oil inventories and offering other crude grades from other fields, Saudi officials said.

No casualties were reported at the sites even though thousands of workers and contractors work and live in the area.

Saudi said it would ensure full oil supply commitments to its customers. The kingdom ships more than 7 million bpd to global destinations every day, and for years has served as the supplier of last resort to markets.

Saudi Arabia's ability to quickly restore oil production after the attacks, which hit at the heart of the Saudi energy industry and intensified a decades-long struggle with arch-rival Iran, would demonstrate an important degree of resilience to potentially very damaging shocks, Moody's said last week.

Aramco is getting ready for an initial public offering possibly later this year. Aramco has a meeting with analysts scheduled for Wednesday at the company's headquarters in Dhahran, two sources said.

(Editing by Louise Heavens and Susan Fenton)