A senior Saudi prince has launched an unprecedented call for change in the country’s leadership, as it faces its biggest challenge in years in the form of war, plummeting oil prices and criticism of its management of Mecca, scene of last week’s hajj tragedy.

The prince, one of the grandsons of the state’s founder, Abdulaziz Ibn Saud, has told the Guardian that there is disquiet among the royal family – and among the wider public – at the leadership of King Salman, who acceded the throne in January.

The prince, who is not named for security reasons, wrote two letters earlier this month calling for the king to be removed.