KT Corp., South Korea's top fixed-line and No. 2 mobile operator, said Friday its third-quarter net profit plunged 63 percent from a year earlier due to a decline in sales and currency losses.

Net profit reached 136 billion won ($128 million) in the July-September period, compared with 369 billion won a year earlier, the Seoul-based company said in a regulatory filing.

Sales fell 7.3 percent on-year to reach 5.73 trillion won over the cited period, while operating income surged 23 percent to 307 billion won, it said.

The third-quarter earnings of the mobile operator were released before the stock market opened. (Yonhap News)