SEOUL (AFP) - State prosecutors on Friday raided the offices of South Korea's top fixed-line operator and number two mobile carrier, KT Corp, as part of an ongoing corruption probe, a company spokesman said.

Investigators collected computer hard drives and documents from the company's three major offices in Seoul and elsewhere, in the second such raid in 10 days.

Yonhap news agency said the private residences of five KT executives were also searched.

The focus of the probe is breach of trust charges filed against KT chairman Lee Suk Chae, alleging the existence of a slush fund and bad investment decisions that cost the firm hundreds of millions of dollars.

Lee, a confidante of former president Lee Myung Bak, has dismissed the allegations as "groundless".

KT said in a regulatory filing Friday that its third-quarter net profit plunged 63 percent from a year earlier to 136 billion won (S$158 million).

Sales fell 7.3 percent on-year to 5.73 trillion won.