Saudi Arabia\'s ailing Crown Prince Sultan bin Abdul Aziz has undergone an operation in a New York hospital, an official at the kingdom\'s consulate in the US metropolis told AFP on Wednesday. \"He is in New York. He has been operated on,\" said the official, who declined to be named discussing private matters of the royal family and did not provide further details. Sultan, who is believed to be in his eighties and has served as defense minister for the past five decades, has been receiving medical treatment for the last two years. The nature of his illness officially has never been revealed, although analysts and diplomats believe it to be cancer. The official Saudi Press Agency reported in mid-June that the crown prince would make a private visit to the United States, during which he would undergo a medical examination. Sultan, who is the half-brother of King Abdullah, has spent several lengthy stays outside Saudi Arabia in recent years, returning from Morocco to the kingdom, a key US ally, last November shortly before the king left to the United States for treatment of a back ailment. The 86-year-old monarch\'s advanced age and the health of the crown prince have highlighted the delicate issue of succession in the kingdom, a major player in Middle East politics and the world\'s number one oil supplier. Prince Nayef, Sultan\'s full brother and considered second in line to the throne, has also had unspecified treatment in the past 20 months. Now in his mid-70s, Nayef has been interior minister for 35 years.