South Korea decided Friday to purchase 40 Lockheed Martin's F-35A stealth fighters for four years starting in 2018, with an option to buy 20 more later depending on the security situation and budget, Yonhap News Agency reported. Joint Chiefs of Staff (JCS) Chairman Choi Yun-hee held a meeting of top commanders in Seoul to approve the plan to buy the 40 F-35 Block 3s, which are capable of conducting air-to-air and air-to-ground missions with internal carriage and external stations for missiles and bombs, the report said. As the F-35 is sold only through the US foreign military sales program, the Defense Acquisition Program Administration is expected to purchase the aircraft through a government-to-government deal and without an open bid, the report said. The total budget hasn't been confirmed as the program's condition requires a foreign government to pay the amount specified by the US government for the F-35s at the time of payment. Seoul had initially assigned KRW 8.3 trillion (USD 7.2 billion) for the past program for 60 jets, the move comes as the Air Force has asked the government to buy the combat aircraft with a lower radar cross section, one of the key stealth functions, and advanced avionic warfare capabilities. "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," JCS spokesman Eom Hyo-sik was quoted as saying in a briefing. The South Korean military will also use the aircraft to effectively deal with provocations, 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. Lockheed Martin's F-35 is still under development for the US military, the decision comes as calls have risen to acquire the fifth-generation jet as the Korean Peninsula is encircled by China and Japan, which are at odds with each other over territorial disputes and seek to expand their military power. Russia is preparing to equip its Air Force with stealth jets to counter the US F-35s and F-22s.