Saudi Arabia's powerful Crown Prince Mohammed bin Salman on Tuesday vowed to restore "moderate, open" Islam in a kingdom known for its ultra-conservative rule.

"We are returning to what we were before -- a country of moderate Islam that is open to all religions and to the world," he said at an economic forum in Riyadh.

"We will not spend the next 30 years of our lives dealing with destructive ideas. We will destroy them today," he added.

"We will end extremism very soon."