The US military's futuristic F-35 fighter jet remains dogged by dangerous problems sure to further complicate what is already the most expensive weapons project in history, a Pentagon report said.

The plane, which boasts a version that can take off and land vertically, is supposed to form the backbone of the military's future fighter fleet, ensuring US dominance in the skies for years to come with radar-evading technology.

The military has already taken delivery of dozens of the planes, but new batches continue to be refined and tested.