Saudi Arabia's King Abdullah is in good shape and began walking shortly after undergoing an operation last week, Interior Minister Prince Nayef bin Abdul Aziz said in a newspaper report on Sunday.

Nayef, the king's half-brother considered second-in-line to the throne, said the 86-year-old king was walking "outside" his New York City hospital on his own feet after his operation Wednesday for a herniated disc, the reports said.

The prince gave no indication of whether the king had been discharged from New York Presbyterian Hospital, nor when he would be returning to the Saudi kingdom he has now ruled for five years.

King Abdullah left Riyadh on Monday for the operation.

Despite the unusual level of transparency about his ailment, the news sparked worries among the population over the reformist monarch's long-term health and the overall make-up of the royal family in government.

The leading princes of the government, including Crown Prince Sultan bin Abdul Aziz, are mostly in their 70s and 80s and have held their jobs for decades.

Many are believed suffering chronic ailments that have not been reported publicly