The chief of the country's top intelligence agency asserted Monday that it has never monitored citizens, vowing to step down from his post if there is truth to the allegation, according to a lawmaker.

Lee Byung-ho, the head of the National Intelligence Service, told lawmakers in a closed-door briefing at the National Assembly that the NIS has never carried out illegal surveillance of ordinary citizens, according to Won Yoo-chul, floor leader of the ruling Saenuri Party.

Nanatech Ltd. is accused of purchasing the hacking software programs from an Italian hacking firm in 2012 on behalf of the NIS.

The software programs use Remote Control System technology, which allows hackers to manipulate and track smartphones and computers by installing spyware.

Opposition lawmakers raised the allegation that the NIS monitored citizens using the RCS to penetrate the country's most-popular mobile messenger KakaoTalk.

At a separate meeting held at the National Assembly, Choi Yang-hee, minister of science, ICT and future planning, said he does not consider RCS programs a monitoring device.

"I think the software is a material that is not a monitoring device," Choi said.

The NIS has said it bought the programs that can be used to hack into up to 20 mobile phones simultaneously and said the programs are designed to work through the Italian company.

The NIS has also said that it used most of the programs to strengthen cyber warfare capabilities against North Korea. (Yonhap)