New York ( CNN ) -- The heir to the Saudi throne , Crown Prince Sultan bin Abdulaziz Al-Saud , died in a New York hospital early Saturday , officials said , raising succession questions in the key oil-producing country at a time of regional turmoil . Sultan , the half-brother of King Abdullah , was thought to be in his 80s . He had been ill for some time -- various reports indicated that he was battling cancer -- and was receiving treatment in New York . Saudi television broke into normal programming early Saturday to announce the death . It broadcast Quranic verses and footage of pilgrims in the holy city of Mecca . Sultan 's body will be flown back to Saudi Arabia and a burial is scheduled for Tuesday . He had served for decades as the Saudi defense minister . President Barack Obama called him a `` valued friend '' of the United States . `` He was a strong supporter of the deep and enduring partnership between our two countries , '' Obama said . `` On behalf of the American people , I extend my deepest condolences to King Abdullah , the royal family , and the people of Saudi Arabia . Robert Jordan , a former U.S. ambassador to Saudi Arabia , called Sultan a `` staunch ally . '' `` His passing marks the end of a significant era in Saudi Arabia , '' he said . `` The steps taken to select a new Crown Prince will be scrutinized by the world and will provide insight into King Abdullah 's vision for future leadership of the Kingdom . '' Ascension to the Saudi throne does not pass from father to son . Rather , it 's a complex process and decisions are always cloaked in secrecy in the conservative kingdom . King Abdullah set up the Allegiance Council in 2006 to allow for more transparency in succession . It is unclear when this group , made up of members of the royal family , will be employed to make a decision on the next crown prince . Sultan 's death leaves his brother Nayef , a reputed conservative , as the likely successor to the king . Abdullah appointed Nayef in 2009 as the country 's second deputy prime minister , a post held by the second in line to the throne . Nayef has been the interior minister since 1975 and as such , he oversaw the kingdom 's counterterrorism efforts . Saudi Arabia is one of the only countries that has truly dismantled a domestic al Qaeda network , said Christopher Boucek , a Saudi expert at the Carnegie Endowment for International Peace . `` Nayef is widely seen as a hard-line conservative who at best is lukewarm to King Abdullah 's reform initiatives , '' said a classified U.S. Embassy cable leaked by the website WikiLeaks . `` However , it would be more accurate to describe him as a conservative pragmatist convinced that security and stability are imperative to preserve Al-Saud rule and ensure prosperity for Saudi citizens , '' the cable said . But Boucek said little has changed . `` The king is still in charge , and nothing will change until the throne passes from him to the next brother . '' Gregory Gause , a University of Vermont professor who has authored books on the Gulf states , said Nayef is hardly one to blaze a path for political reform , but that 's not to say Saudi Arabia will feel any reverberations . `` There is truth to the idea that Nayef is not someone who sees political reform as a major goal of the government , '' Gause said . `` But I do not want to say that if he were to become king , he would act in the same way as he is now . '' Saudi Arabia is not immune to the sort of popular uprisings that have brought down regimes in Tunisia , Egypt and Libya . The nation suffers from the same political and economic issues , Gause said . But the difference , he said , is that Saudi Arabia is wealthy and the king has recently deployed huge amounts of money for housing and salaries . Also Saturday , Abdullah left a hospital in Riyadh following successful back surgery , the Saudi Press Agency reported . Abdullah , 87 , will complete his recuperation at the royal palace . It was the monarch 's third back surgery in the past year . Meanwhile , Saudi Arabia 's leadership mourned Abdullah 's half-brother . `` Crown Prince Sultan lived his life in service of his country and also serving the Arab people and the people of Saudi Arabia , '' said Saleh Al-Namla , a member of Saudi Arabia 's Shura Council . `` He was very much loved by the country . '' He took a leading role in Saudi Arabia 's involvement in the 1991 Gulf War against Iraq , heading a coalition of about half a million troops from more than 30 countries . Of his many children , perhaps the best known internationally is Prince Bandar , Saudi Arabia 's former ambassador to the United States . Bandar served as ambassador from 1983 to 2005 and was friends with the family of former President George W. Bush . CNN 's Jamie Crawford , Mohammed Jamjoom , Moni Basu , Nic Robertson and Rima Maktabi contributed to this report .
King Abdullah leaves Riyadh hospital after back surgery . President Obama says the United States has lost a 'valued friend ' Sultan had been ill for some time and died in a New York hospital . The U.S. State Department said it was "deeply saddened" by news of Abdullah's death.