(Adds detail, background)

* Oct Iran crude imports at 902,987 T, up 73.8 pct y/y

* Jan-Oct crude imports from Iran, up 110 pct y/y

* Total Oct crude imports at 11.59 mln T, up 3.6 pct y/y

By Jane Chung

SEOUL, Nov 15 (Reuters) - South Korea's Iranian crude oil imports soared 73.8 percent in October from a year ago as Tehran continued to boost its output to pre-sanction levels.

Seoul brought in 902,987 tonnes of Iranian crude, or 213,513 barrels per day (bpd), compared with 519,620 tonnes imported during the same month a year ago, customs office data showed on Tuesday.

The world's fifth-largest crude importer, shipped in 10.72 million tonnes of Iranian crude in the first 10 months of 2016, or 257,560 bpd, more than double from 5.1 million tonnes a year earlier.

But South Korea, one of Iran's top four Asian buyers, imported less Iranian crude in October from a month ago, about 39.3 percent lower from 1.49 million tonnes in September mainly due to refinery maintenance.

SK Incheon Petrochem, owned by SK Innovation Co Ltd , was fully shut down for maintenance from Sept.19 through Oct.28.

South Korea's crude oil import data usually includes condensate, but it does not provide a breakdown.

Along with Iran, the Organization of the Petroleum Exporting Countries (OPEC) also pumped out more in October led by Libya, Nigeria and Iraq - countries that have sought to be exempted from the producer group's freeze talks. The October output was 33.64 million bpd, up 240,000 bpd from the previous month.

Overall, Asia's fourth-largest economy imported 11.59 million tonnes of crude oil last month, or 2.74 million bpd, up 3.6 percent from 11.18 million tonnes a year ago, according to the customs data.

South Korea shipped in 118.44 million tonnes of crude in the January-October period of 2016, or 2.85 million bpd, up 4.4 percent from 113.49 million tonnes last year.

Final data for October crude oil imports will be released by state-run Korea National Oil Corp later this month.

(Reporting by Jane Chung; Editing by Michael Perry) ((jane.chung@thomsonreuters.com; +82 2 3704 5667; Reuters Messaging: jane.chung.thomsonreuters.com@reuters.net))