RIYADH (Reuters) - Saudi Arabia's King Abdullah appointed his son Abdul-Aziz to the post of deputy foreign minister on Friday, in a move that appears to strengthen the king's hand in Saudi foreign policy amid jostling for positions among senior princes. The state news agency said the move was part of a series of appointments made by the king, who is in his 80s. Saudi Arabia is facing a succession struggle as senior princes in the absolute monarchy manoeuvre to secure their power bases. King Abdullah and his half-brother Crown Prince Sultan, the country's defence minister who is also in his 80s, and have spent time abroad to treat health problems in recent years.