1   any articles or materials the export of which is prohibited by
 
2    this Act, or on articles or materials carried by an American
 
3 can vessel in violation of subsection (a) of this section,
 
4 shall be not deemed an American interest therein, and no
 
5 insurance policy issued on such articles or materials and no
 
6 loss incurred thereunder or by the owner of the vessel
 
7 carrying the same shall be made a basis of any claim put
 
8 forward by the Government of the United States.
 
9    "(c) The President shall from time to time by proocla-
 
10 tion extend such restrictions as are imposed under the authority
 
11 of this section to other states as and when they may be
 
12 declared to become beligerent states under proclamations
 
13 issued under the authority of section 1 of this Act.
 
14   "(d) The President may from time to time change,
 
15 modify, or revoke in whole or in part any proclamations is-
 
16 sued by him under the authority of this section."