* A brother of Saudi king objects to deputy PM nomination

* He says nomination may make interior minister crown prince

* Prince Talal urges king to clarify his appointment

By Souhail Karam

RIYADH, March 28 (Reuters) - A brother of Saudi Arabia's King Abdullah has started a rare public debate over the succession by questioning the appointment of the kingdom's interior minister as second deputy prime minister -- a position that would normally place him second in line to the throne.

The statement, by Prince Talal bin Abdul-Aziz, came after the Saudi royal court announced on Friday the appointment of Prince Nayef bin Abdul-Aziz as second deputy prime minister, a promotion that means he will run the kingdom when the monarch and crown prince are away.

The role would normally go to First Deputy Prime Minister Crown Prince Sultan, but he is convalescing in the United States after surgery earlier this year.

Prince Talal said the monarch needs to make sure the appointment served purely an "administrative purpose".