South Korea's current account surplus narrowed in August from the previous month on smaller trade gains, but it logged a surplus for the 19th straight month, the central bank said Friday.

The current account surplus reached $5.74 billion in August, down from $6.77 billion the previous month, according to the Bank of Korea (BOK). The current account is the broadest measure of cross-border trade.

The surplus narrowed in August from the previous month, but Korea has maintained a current account surplus since February 2012.

The combined surplus amounted to $42.28 billion in the first eight months of this year.

In July, the BOK revised up its 2013 current account surplus estimate to $53 billion, which would be a record high, if realized.

"Given the surplus trend, it seems that there would be no problem in achieving the full-year estimate," Jung Young-taek, the director general of the BOK's economic statistics division, told reporters.

The underlying trend of the surplus is likely to lend support to the local currency, which has risen more than 3.5 percent against the U.S. dollar since mid-May, analysts say.

The current account surplus and a pile-up in the foreign reserves are giving solace to South Korea as some emerging markets, including India and Indonesia, are suffering from foreign capital outflows and subsequent currency weakness.

But Asia's fourth-largest economy is also raising its alertness against an influx of massive foreign capital as it could serve as a destabilizing factor for the economy.

The balance of Korea's goods posted a surplus of $5.33 billion in August, smaller than the surplus of a revised $5.67 billion in July.

In August, overseas shipments rose 7.9 percent on-year to $46.29 billion and imports gained 1.4 percent to $40.96 billion.

The service account, which includes outlays by South Koreans on overseas trips, posted a surplus of $100.6 million last month, compared with a surplus of $357 million in July.

The primary income account, which tracks wages of foreign workers and dividend payments overseas, logged a surplus of $475.2 million in August, down from a surplus of $776.5 million the previous month.

The capital and financial account, which covers cross-border investments, posted a net outflow of $7.69 billion in August, compared with a net outflow of a revised $7.32 billion in the previous month, the BOK said.

Foreigners' investment in local bonds logged a net inflow of $610 million last month, sharply down from a net inflow of $3.03 billion in July. (Yonhap News)