A US veteran who lost his genitals and much of his pelvic region in a bomb blast in Afghanistan, has undergone the world's most extensive penis transplant.

While there have been three other successful penis transplants in the past, none of the others have been as complex and involved as much surrounding tissue.

Surgeon's at Johns Hopkins University surgeons in Baltimore, Maryland, rebuilt the man's entire pelvic region - transplanting a penis, scrotum and part of the abdominal wall from a deceased donor - in a highly experimental 14-hour operation in March.

Four weeks later and the patient - who wishes to remain anonymous - is "doing extremely well", Dr Richard Redett from the university's Department of Plastic and Reconstructive Surgery said.

He continued: "He's up, he's walking, he's showing no signs of infection or rejection, and will hopefully be discharged home at the end of this week."

Dr Redett added that in time, the veteran's ability to urinate normally should return as would his "sexual function".

Following his recovery, the patient will not be able to have children, as testicles were not included in the scrotum transplant.

However, the veteran said that the operation has left him "finally" feeling "more normal".

The university said it has screened other veterans with similar injuries to see if they could receive reconstructive transplants too.

The operation was also experimental, with the patient receiving a bone marrow infusion from the donor, in a bid to help the recipient's immune system better tolerate a transplant and enable him to take one anti-rejection drug instead of several.