The city-state last year said it planned to buy four of the jets, with an option to purchase eight more, picking the Lockheed Martin model over rivals from Europe and China.

Despite its small size, Singapore has one of the region's best equipped armed forces and spends a large chunk of its national budget on defence.

The State Department had approved the jet sale, said the US Defense Security Cooperation Agency, adding Congress had been notified and must now also give the green light.

"Singapore is a strategic friend and major security cooperation partner and an important force for political stability and economic progress in the Asia-Pacific region," said the agency.

It added that the deal "will not alter the basic military balance in the region".

The affluent city-state spent several years assessing which fighter jet should replace its ageing fleet of F-16s before choosing the F-35s.

It is a supersonic plane whose advanced stealth characteristics allow pilots to avoid detection by radars, according to Lockheed Martin.

Its advanced electronic warfare capabilities enable pilots to locate and track enemy forces, jam radars and disrupt attacks.

The Singapore military also has F-15 fighter jets, Apache helicopters and submarines in its arsenal.

mba/sr/ecl

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LOCKHEED MARTIN