How can i lock an user from a package?

Hi
 I need to lock an oracle user from inside a package, so i can't use ALTER instruction... If i do

ALTER USER username ACCOUNT LOCK;

it throws the following:

PLS-00103: Encountered the symbol "ALTER" when expecting one of the following:

   begin declare exit for goto if loop mod null pragma raise    return select update while Received on Tue Nov 30 2004 - 13:59:04 CST