Create table problem using Dynamic Query

[Ach]

Hi all,
I want to create a temporary table within a stored procedure so I decided to do it using a dynamic query:

create or replace procedure p1
as
 begin
 execute immediate 'CREATE GLOBAL TEMPORARY TABLE tt(id number(2))';
 end;
/

It created successfuly but when I execute that procedure I got:

SQL> exec p1;
BEGIN p1; END;

*
ERROR at line 1:
ORA-01031: insufficient privileges
ORA-06512: at "SCOTT.P1", line 4
ORA-06512: at line 1

While I can create that table using the same user without any problem!
My question is:What privilege should I grant to user(minimum of privileges please! ) to execute that procedure successfuly?
-Thanks