The answer was given previously:

All the schools which are USMLE approved are listed above. Any school approved by the US is also approved for USMLE.

As far as transferring from a Pakistani medical college to a US one, it is generally not possible to transfer due to the huge difference in timing of curriculum, insane competitiveness of US schools, and the fact that all US medical schools require completion of a bachelors degree prior to gaining admission.