S.Korea shares gain for third straight week on vaccine cheer

* KOSPI rises, foreigners net buyers

* Korean won strengthens against U.S. dollar

* South Korea benchmark bond yield rises

* For the midday report, please click

SEOUL, Nov 20 (Reuters) - Round-up of South Korean financial markets:

** South Korean shares closed higher on Friday, gaining for a third straight week as optimism around potential COVID-19 vaccine breakthroughs offset concerns over rising cases in South Korea. The Korean won strengthened and the benchmark bond yield rose. ** By 0630 GMT, the benchmark KOSPI rose 6.08 points, or 0.24%, to 2,553.50. For the week, the index gained 2.4%. ** A U.S. official said COVID-19 vaccines from Pfizer Inc and Moderna Inc could be ready for U.S. authorization and distribution within weeks, strengthening hopes of a recovery from the pandemic-induced economic slump.

** AstraZeneca and Oxford University also said their potential COVID-19 vaccine produced a strong immune response in older adults.

** Still, sentiment took a hit after South Korea’s prime minister warned of strict COVID-19 curbs returning if the current level of infections was not contained soon and pleaded with the public to avoid social gathering.

** Also capping gains was Thursday’s call by U.S. Treasury Secretary Steven Mnuchin to end pandemic relief for struggling businesses. ** Foreigners were net buyers of 102.3 billion won worth of shares on the main board. Foreigners were net buyers for the 12th straight session, their longest buying spree since January 2017. ** The won was quoted at 1,114.3 per dollar on the onshore settlement platform, 0.12% higher than its previous close at 1,115.6. ** The trading volume during the session in the KOSPI index was 1,115.84 million shares. Of the total traded issues of 905, the number of advancing shares was 549. ** In money and debt markets, December futures on three-year treasury bonds fell 0.01 points to 111.65. ** The most liquid 3-year Korean treasury bond yield rose by 0.9 basis points to 0.963%, while the benchmark 10-year yield rose by 0.3 basis points to 1.605%. (Reporting by Cynthia Kim; Editing by Devika Syamnath)