SEOUL (AFP) - The operator of South Korea's dominant instant-messaging service Kakao Talk has vowed to put privacy before the law and deny state prosecutors access to the messages of its users when conducting investigations.

The Supreme Prosecutors' Office and various government agencies, including the National Police Agency, last month announced "proactive" measures to prevent the spread of false and malicious online postings.

The crackdown came after President Park Geun Hye, whose personal life has been a topic of online comment in recent months, complained that such posts were socially divisive and destructive.

But in a news conference late Monday, the co-chief executive of Daum Kakao, Lee Sirgoo, publicly apologised to users who have begun defecting to other messaging apps because of concerns about its commitment to privacy.

"We regret that Daum Kakao failed to understand the anxiety of Kakao Talk users," Lee said.

"In order to prevent ourselves from making the same mistake, we will make privacy our top priority when there is clash between privacy and law," he added.

Lee said the firm had ceased responding to prosecutors' warrants since October 7, and would continue to do so in the future.

"If our decision is a violation of the law, I as the head of Daum Kakao, will bear any responsibility," he added.

Out of a total population of 50 million, around 35 million South Koreans are estimated to use Kakao Talk.

It was not clear if Daum Kakao's decision to cease entertaining prosecutors' access requests would spark a legal confrontation with the government.

In a meeting with senior staff on Tuesday, Prosecutor General Kim Jin Tae voiced surprise at Lee's comments and insisted there was a misunderstanding over the extent of his office's powers.

"There is no legal basis for us to monitor everyday private conversations on Kakao Talk," Kim was quoted as saying by Yonhap news agency.

"The prosecution only obtains court-approved warrants to check conversations related to major crimes like kidnapping,human trafficking and drugs," he said. "Real-time monitoring is technically impossible."