Israeli Defence Minister Ehud Barak approved in principle on Sunday the purchase of 20 U.S.-built radar-evading stealth fighters in a deal worth $2.75 billion, defence ministry officials said.

The F-35 warplanes are expected to be delivered between 2015 to 2017, an Israeli defence official said.

Israeli leaders have spoken of arch-foe Iran potentially developing a nuclear weapon by mid-decade, suggesting that the F-35s would not be used for any preventive action, but rather to bolster the country's deterrence.

A ministry statement said Barak "approved in principle the recommendations of the Israel Defence Forces and the Defence Ministry to move ahead" with the purchase.

The stealth fighter, made by Lockheed Martin Corp , "will afford Israel continued air superiority and maintain the technological edge in our region", the statement quoted Barak as saying.
The defence official said Israel planned to buy initially 20 planes, estimating the total price tag at $2.75 billion, to be covered by an annual U.S. defence grant of $3 billion.

Officials predicted final approval of the deal could be given by the end of September by a panel of Israeli government ministers.

Israel would be the first foreign country to sign an agreement to buy the F-35, or Joint Strike Fighter, outside the eight international partners that have helped to develop the plane.

The deal has been in negotiations since September 2008, when the Pentagon first approved the sale of 25 fighters with an option for more in the coming years.

The F-35 is designed to avoid detection by radar and could play a role in any Israeli effort to knock out what it regards as the threat to its existence posed by Iran's nuclear programme. Tehran denies Western and Israeli allegations that it is trying to produce atomic weapons.

Defence Ministry Director-General Udi Shani said incorporation of Israeli technologies into the F-35 had played a role in Barak's decision to buy the aircraft.

Israel, widely assumed to have the Middle East's sole nuclear arsenal, also had considered a cheaper option -- the purchase of a modified version of Boeing's F-15 fighter, an aircraft it already deploys.