Why dbms_lock.sleep is not working for non-sys users?

PL/SQL procedure successfully completed.  

SQL> show user

USER is "SYS"

SQL> connect tsuser

Enter password:

Connected.

SQL> exec dbms_lock.sleep(10);

BEGIN dbms_lock.sleep(10); END;  

      *

ERROR at line 1:

ORA-06550: line 1, column 7:

PLS-00201: identifier 'DBMS_LOCK' must be declared

ORA-06550: line 1, column 7:

PL/SQL: Statement ignored    

SQL>   Thanks  

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