SEOUL, Nov 15 (Reuters)

South Korea's October imports of Iran oil remained at zero for a second straight month ahead of U.S. sanctions against Iran that came into effect on Nov.5, customs office data showed on Thursday.

In September, South Korea's imports of Iran oil fell to zero for the first time in six years as South Korean buyers halted purchases from the Middle Eastern due to uncertainty over whether they would receive a waiver from the U.S. government.

South Korea was granted a temporary waiver from U.S. sanctions, along with seven other countries, to purchase Iran oil. The sanctions aim to force Tehran to stop not only its nuclear and ballistic missile program but also its involvement in regional conflicts in Syria.

The country's final October crude oil imports data by state-run Korea National Oil Corp (KNOC) is due for release later this month.

South Korea can buy up to 200,000 barrels per day of Iran oil, mostly condensate, according to sources with knowledge of the matter.

In the January-October period of the year, the country's imports of Iranian oil halved to 7.15 million tonnes, from 15.70 million tonnes in the same period a year earlier, according to the data. The data does not provide a breakdown of imports by types.

Overall, South Korea imported 13.07 million tonnes of crude oil in October, up 5.1 percent from 12.44 million tonnes from a year earlier.

Oil shipments from Saudi Arabia, South Korea's top oil supplier, almost doubled to 4.17 million tonnes in October, from 2.68 million tonnes from a year earlier.

In the first 10 months of the year, 123.52 million tonnes of crude oil were imported to South Korea, up 0.5 percent from 122.88 million tonnes on year.

(Reporting By Jane Chung; Editing by Michael Perry)