Future exports of the US advanced F-22 fighter may become difficult, according to US Air Force chief of staff General Norton Schwartz.

The chief of staff said that pragmatic obstacles such as technical, legal and timing aspects would affect the export.

The obstacles include a legal ban on F-22 exports overseas, the high costs that would be incurred for designing an export version of the plane and the issue of the production line being still open by the time any exports were approved.

Opponents say the issue can be dealt with since a large percentage of the components on the F-22 are the same as the F-35.

The F-22 is a multi-role fighter capable of simultaneously carrying out air-to-air and air-to-ground combat missions.

The US Department of Defense has planned to halt the production of the F-22 after the production of 187 planes, despite the military requirement for 243, due to budget constraints.

Recent changes such as North Korean missile launches and continued interest by Japan for F-22s had softened the opposition to the export of the fighters.