South Korea has chosen a state-run aircraft maker as the sole preferred bidder for a contract to develop a midlevel fighter jet for about $7.8 billion with the help of Lockheed Martin Corp.

Officials say it's South Korea's biggest-ever weapons development project.

Seoul's Defense Acquisition Program Administration said Monday it'll negotiate with Korea Aerospace Industries about detailed terms for the contract.

Defense agency officials say Lockheed Martin, which last year won the rights to provide 40 F-35A fighter jets, is to help the KAI develop the jet.

They say the $7.8 billion is only for system development and the production of prototype jets by 2025.

They say they eventually want to introduce 120 such fighter jets to replace the country's aging fleets of F-4 and F-5 fighter jets.