Protesters shout slogans during a rally against a meeting of senior military officers to choose South Korea's next-generation fighter jets in front of the Defense Ministry in Seoul, South Korea, Friday, Nov. 22, 2013. South Korea made a decision Friday to purchase 40 Lockheed Martin's F-35A fighters over four years from 2018, with an option to buy 20 more later depending on the security situation and budget, the Joint Chiefs of Staff said. (AP Photo/Ahn Young-joon)SEOUL, Nov. 22 (Kyodo) — South Korea will purchase 40 Lockheed Martin F-35A stealth fighter jets and an additional 20 combat planes from the United States starting in 2018, South Korea's Joint Chiefs of Staff said Friday.

"The F-35A will be used as a strategic weapon to gain a competitive edge and defeat the enemy in the early stage of war," Joint Chief of Staff spokesman Eom Hyo Sik was quoted as saying by Yonhap News Agency following a statement made by North Korea earlier in the day, saying that Pyongyang would turn the South's presidential office into a "sea of fire."

"The South Korean military will also use the aircraft to effectively deal with provocations," Eom said in a briefing.

According to Yonhap, JCS Chairman Choi Yun Hee held a meeting of top commanders to approve the plan to buy the F-35A stealth fighter jets that are capable of conducting air-to-air and air-to-ground missions with internal carriage and external stations for missiles and bombs.

As the F-35 is sold only through the U.S. foreign military sales program, the South Korean Defense Acquisition Program Administration is expected to buy the aircraft through a government-to-government deal without an open bid.

The budget has not been confirmed as the conditions set by the U.S. foreign military sales program require a foreign government to pay the amount specified by Washington for the F-35s at the time of payment.

For an additional 20 jets, the South Korean government will reconsider the required operational capability and security situations with a goal of deployment between 2023 and 2024, Eom said, giving Boeing and the European Aeronautic Defense and Space Company, which participated in the past bidding, an opportunity to secure a contract.

"The JCS decided to buy 40 jets first to minimize the security vacuum and purchase the remaining 20 after reassessing the required operational capability in accordance with the changing security situations and aerospace technology," Air Force Brig. Gen. Shin Ik Kyun was quoted by Yonhap as saying.

South Korea has been seeking to develop a much larger indigenous fighter jet program with the help of major defense contractors, but the plans have been delayed largely due to budget constraints.