Debt held by South Korea's central bank grew 3.1 percent in 2013 from the previous year while its net profit fell to the lowest in six years amid the local currency's gain, data showed Thursday. The debt of the Bank of Korea (BOK) amounted to 448.4 trillion won (US$417 billion) as of the end of last year, compared with 435 trillion won the previous year, according to the data compiled by the central bank.