WASHINGTON (BNS): Even as Lockheed Martin announced the successful flight test of its F-35B Lightning II short takeoff/vertical landing (STOVL) stealth fighter aircraft, US has put off its plan to buy 10 F-35s in 2011.

The US had earmarked a total of $2.8 billion to buy the fifth-generation combat aircraft. Now, the fund would be used for the aircraft's development, Defence Secretary Robert Gates has said according to a news report in Bloomsberg.

The US has also decided against buying 122 F-35s through financial year 2015, the report said.

The combat aircraft is being developed by the US defence major Lockheed Martin in partnership with eight other countries.

Lockheed Martin had last week reported the successful flight test of the aircraft's short takeoff/vertical landing (STOVL) version. The F-35B would replace the US Marine Corps AV-8B STOVL fighters, F/A-18 strike fighters and EA-6B electronic attack aircraft, it had said.

Gates, however, has suggested that US should spend an additional $2.4 billion in 2011 and 2012 to buy 26 F/A-18E/F planes.

The F-35 is a fifth-generation multi-role stealth combat aircraft capable of performing close air support, tactical bombing and air defence missions. It is being designed to replace the existing fleet of fighter aircraft of the nine partnering countries.

The project had got a boost when Britain had recently announced to buy its third F-35B Lightning II fighter aircraft for operational testing and evaluation.

Pentagon has expressed concern over the escalating cost of the aircraft and likely delay in its delivery schedules.