My circular M.200. 
JAPAN (i) The possibility that the Japanese may be contemplating dangerous action in relation to Thailand, and a message now received from the Thai Prime Minister  have made it imperative that we should take up at once with the United States Government the advisability of a warning being conveyed to the Japanese before the latter are committed to a further move. We also wish to raise with the United States Government at the earliest suitable moment the general question of an assurance that in the event of war with Japan we may count upon their armed support, see my telegram to the Commonwealth Government 515.  A third approach is also necessary since such information as has reached us as to the manner in which the United States Freezing Order is to be applied (see my Circular M.1935) suggests that there has been a departure from the policy outlined to us before the freezing order was issued (see my Circular M. 173 ) with consequent risk that we and the other parts of the Empire may in practice find ourselves ahead of the United States in our restrictions.
(2) My three immediately following telegrams contain instructions which have now been sent to His Majesty's Ambassador at Washington  in regard to each of these aspects, viz.:-
(a) the question of an assurance from the United States;
(b) warning to Japan;
(c) freezing of Japanese assets. 8 The nature of the information reaching us about Thailand and uncertainty in regard to the United States policy over application of the freezing order make (b) and (c) very urgent. (a) is equally pressing but it is a particularly delicate question and informal discussions with the United States Ambassador here  have shown that the method of approach is all important. While, therefore, we have acquainted His Majesty's Ambassador very fully with the point of view of the Dominions and ourselves, we think it necessary as regards (a) to await his observations before giving him definite instructions to take action.