South Korea's foreign currency reserves continued a record-breaking trend last month due to a rise in investment returns, central bank data showed Wednesday.

Forex reserves rose 1.38 billion U.S. dollars from a month earlier to reach a fresh high of 331.09 billion dollars as of the end of August, according to the Bank of Korea. The figure topped the previous record high after breaking the record in the prior month.

The central bank attributed the record-breaking trend to the persistent gain in returns from invested assets. The country's forex reserves stayed above the 300-billion-dollar mark since April 2011 when it breached the level for the first time in its history.

As of the end of July, South Korea was the world's seventh- largest holder of forex reserves following China, Japan, Switzerland, Russia, China's Taiwan and Brazil.

The forex reserves consisted of 302.11 billion dollars of securities, 18.16 billion dollars of deposits, 4.79 billion dollars of gold bullion, 3.43 billion dollars of special drawing rights and 2.6 billion dollars of International Monetary Fund positions.