South Korea's external debt fell in the first quarter due to a weaker won, with the ratio of the short-term foreign debt against the total debt hitting an over 13-year low, the central bank said Wednesday.

The country's external debt totaled US$410.3 billion as of the end of March, down $3.3 billion from three months earlier, according to the Bank of Korea (BOK).

The data marked the lowest reading since $398.7 billion in the fourth quarter of 2011.

The BOK said that foreign investors continued to buy local bonds in the first quarter, but the won's weakness reduced the value of their bond holdings, leading to the decline in the total external debt.

Since last year, foreign investors have snapped up Korean bonds as they were seen as attractive amid aggressive monetary easing moves by major economies and a spate of credit rating upgrades for Korea.

But the local currency turned weaker in the first quarter amid heightened geopolitical risks from North Korea's war threats. The won fell 3.7 percent per the dollar in the first quarter.

In the January-March period, Korea's short-term foreign debt declined to the lowest mark since the fourth quarter of 2006, indicating that the structure of its foreign debt has improved.

The country's short-term external debt amounted to $122.2 billion, down $4.5 billion from three months earlier. But its long-term foreign debt rose by $1.3 billion on-quarter to $288 billion amid foreigners' investment in monetary stabilization bonds sold by the central bank.

Accordingly, the rate of the short-term debt against Korea's total debt reached 29.8 percent as of the end of the first quarter, the lowest since 29.7 percent in the fourth quarter of 1999.

The ratio of the short-term debt against the foreign reserves came in at 37.3 percent as of end-March, the lowest since 34.6 percent in the first quarter of 2006.

The finance ministry said that the government will closely monitor cross-border foreign capital movement in a bid to brace for potential sudden outflows of such foreign funds.

Korea's high short-term foreign debt used to be a major headache whenever a financial crisis cropped up as a surge in foreign debt left local banks vulnerable to external shocks.

South Korea's net external credit reached $134.2 billion as of end-March, up $11.9 billion from the preceding quarter, it noted. (Yonhap News)