South Korea's No. 1 mobile carrier SK Telecom Co. said Monday it has filed a lawsuit against global mobile messenger Viber earlier this year for infringement on four patents held by the company.

"It is true that the lawsuit is going on," an official from SK Telecom told Yonhap, without revealing further details.

"The lawsuit is aimed at protecting the company's patent rights and prevent (our) business models being infringed," SK Telecom said. "We cannot open other details, as the lawsuit is still going on at a court."

Early on Monday, Talmon Marco, the CEO and founder of Viber, told Yonhap News Agency during an interview that SK Telecom had sued his company over alleged violation of four patents. SK dropped one of the cases later, and South Korea's patent office invalidated two others, according to Marco. "We are fighting for one more," he said.

"I think I am very optimistic about our chances of winning. Actually when we got that lawsuit, we were quite surprised," Marco said. "Viber does not compete in Korea. We are not big in Korea... We are thinking they are looking for easier target."

He claimed that SK Telecom's move is to "stop companies like Viber and Kakao Talk from operating and force all Korean users back to short-message-services."

Neither Viber nor SK Telecom elaborated on what patents were involved in the lawsuit.

Viber was launched in 2010 by four Israeli entrepreneurs -- Marco, Igor Megzinik, Sani Maroli and Ofer Smocha. It runs on most major platforms including Windows 8, Android, iOS, Blackberry and Nokia.

Viber currently commands some 360 million users from 193 countries, with services being provided in 38 languages, including English, Hebrew, Japanese and Korean. The service provider was acquired by Japan-based online retailer Rakuten Corp. earlier this year at US$900 million.

Marco visited Seoul to attend the Global ICT Premier Forum, which is being held alongside the 19th International Telecommunications Union Plenipotentiary Conference, referred to as the PP-14. (Yonhap)