Korean banks suffered a 9 percent on-year decline in net profit earned from their overseas operations last year due to deteriorating net interest margins, the country's financial watchdog said Monday.

In 2015, domestic banks posted a combined net income of $572 million from their overseas operations, down from $629 million a year earlier, the Financial Supervisory Service (FSS) said in a statement. 

In a breakdown of their overseas earnings, non-interest income rose 22 percent year-over-year to $469 million in 2015, but interest income fell 6.7 percent to $1.27 billion, the statement said.

Their average net interest margin fell to 1.55 percent last year from 1.72 percent a year earlier. At the end of December, Korean lenders were running 168 overseas subsidiaries, branches and offices in 38 countries, according to the watchdog. (Yonhap)