South Korea is expected to post a record-high trade surplus with the United States this year, customs sources said Monday, sparking woes that Washington may take action to narrow its deficit.

The outlook came as South Korea has posted a trade surplus of $18.1 billion as of Nov. 20, already hovering above a record-breaking annual surplus of $15.2 billion posted in 2012, according to related data released earlier from the Ministry of Trade, Industry and Energy.

It also marked a sharp increase from the surplus of $8 billion tallied in 2008, when the global financial crisis dealt a harsh blow to local exporters.

Such an increase came as the country's exports to the U.S. between Jan. 1 and Nov. 20 this year have grown 6.4 percent on-year to some $54.82 billion, while its imports from the North American country dropped 6.7 percent over the cited period to about $36.69 billion.

South Korea took up 3.3 percent of the combined U.S. trade deficit in the first nine months of 2013, up 1 percentage point from 2.2 percent tallied for all of 2012, making the country the 8th-largest gainer in the U.S. market over the cited period, separate data by Shinhan Investment Corp. showed.

Market watchers said U.S. regulators may accordingly impose pressure on Asia's fourth-largest economy to appreciate the Korean won against the greenback and make efforts to narrow such a trade imbalance between the two countries.

The won traded at 1,063.20 won against the greenback in the first trading session of 2013, but it plunged to 1,159.10 won on June 26. It closed at 1,058.20 won on Friday.

A relatively weaker won makes South Korean goods and services more price-competitive in the overseas market, making them appear cheaper compared to global rivals.

Bank of Korea (BOK) Gov. Kim Choong-soo, however, said in November that South Korea's trade surplus is attributable to other factors. He added that most of the country's gain in trade came from emerging markets and not advanced ones.

South Korea posted a trade surplus for the 22nd consecutive month in November at $4.8 billion, due mainly to the growth in exports of ships and information-technology products, the trade ministry said. (Yonhap News)