In a letter in Arabic addressed to ministers and posted on his website, Prince Alwaleed described the idea of the kingdom tolerating lower prices below $100 per barrel as potentially "catastrophic" for the economy of the desert kingdom.

The letter, first reported online by the FT, is a significant attack on Saudi's highly respected 79-year-old oil minister Ali bin Ibrahim Al-Naimi who has the most powerful voice within the Organisation of Petroleum Exporting Countries (Opec).