SEOUL, Jan 21 (Reuters) - South Korea plans to sell 800 billion won ($670.85 million) worth of treasury bonds via non-competitive bidding in January, the finance ministry said on Friday. The treasury bonds will be issued at pre-announced interest rates, which will be released at 10:20 a.m. (0120 GMT) on Jan. 28. Below are auction details released by the finance ministry in a statement: DATE TENOR AMOUNT Jan 28 2 years 0.20 trln won Jan 28 3 years 0.20 trln won Jan 28 30 years 0.40 trln won ($1 = 1,192.5100 won)