A Baltimore hospital says a wounded US veteran has received the world's most extensive penis transplant.

Doctors at Johns Hopkins University said the transplant included the scrotum and part of the abdominal wall.

They said the patient had the highly experimental transplant last month in a 14-hour operation and said he was recovering well, and expected to leave the hospital later this week.

"We are hopeful that this transplant will help restore near-normal urinary and sexual functions for this young man," WP Andrew Lee, director of plastic and reconstructive surgery at the Johns Hopkins University School of Medicine, said in a media release.

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The patient, who asked not to be identified, survived a blast in Afghanistan a few years ago that devastated his groin and pelvic region.

"It's a real mind-boggling injury to suffer, it is not an easy one to accept," the veteran said.

"When I first woke up, I felt finally more normal … [with] a level of confidence as well."

Three other successful penis transplants have been performed, two in South Africa and one in 2016 at Massachusetts General Hospital.

But those transplants involved only the penis, not extensive surrounding tissue that makes such surgery for combat wounds more difficult.

A diagram showing the complexities of the transplant. ( Supplied: Devon Stuart for Johns Hopkins Medicine )

AP