"Neither Seoul nor Taipei clearly declares their currency intervention, leaving traders to infer it from balance of payments data, or market movements during particular hours of trading," said the newspaper. "The economic footprints of intervention are clear, however. South Korea has a current account surplus of nearly 8 percent of gross domestic product, compared with just 3 percent for China and Japan."

The news came as the US government is considering designating some big trade countries like China and Japan as currency manipulators, given their massive trade surpluses against the United States.

"On behalf of the South Korean government, the Ministry of Strategy and Finance and the Bank of Korea sent a letter of protest to the FT on Wednesday," said Lee Young-joo, a spokesperson of the finance ministry. "We wrote our opinion against the FT's reports."

In the letter, the government stressed that it has not intervened in the foreign exchange market to depreciate the Korean won and the International Monetary Fund and the US government have already acknowledged that.

South Korea's Finance Minister Yoo Il-ho earlier said that there is no possibility that South Korea would be designated as a currency manipulator under the current US guidelines. The country met only two out of three criteria to be considered a currency manipulator.

Asia's fourth-largest economy posted $23.3 billion in trade surplus with the US last year, accounting for 26 percent of the country's total trade surplus. (Yonhap)