The National Intelligence Service made the report to a closed-door meeting with members of a parliamentary intelligence committee, Yonhap quoted committee members as saying.

North Korea was not among the 16 countries, which include South Korea, the United States, Japan, and Guatemala, Yonhap said.

The cyber attacks have been traced to 86 Internet Protocol addresses in the countries, intelligence officials reportedly told the committee.

As for North Korea's involvement in the attacks, the intelligence agency suspects the North, but it is too early to say with certainty because an investigation is still going on, the report said.

Its suspicion that North Korea or its sympathizers may be behind the attacks is based on the fact that the attacks targeted conservative groups, and that the North issued a statement warning of cyber warfare last month, and methods used by certain hackers.

The North's committee for the Peaceful Reunification of Korea said in a statement on June 27 Pyongyang was "fully ready for any form of high-tech war."

The North Korean statement was in protest of South Korea's plan to participate in the U.S.-led exercise "Cyber Storm," that simulates a federal response to a major cyber attack, according to Yonhap.