In early 1949, a Draft Report by the US National Security Council determined that while Formosa and the Pescadores were under the de facto control of the Chinese Nationalists, these islands were still legally a portion of the Japanese Empire.
1949年初，美國國家安全委員會的報告草稿確定，實際上雖然福爾摩沙和澎湖是在中國國民黨的控制之下，但這些島嶼在法律上仍是日本帝國的一部分。
Draft Report: by the National Security Council
Date: January 19, 1949
Subject: U.S. policy with respect to Formosa and the Pescadores
報告草稿： 國家安全委員會編寫
日期： 1949年01月19日
主旨： 美國對福爾摩沙和澎湖的政策
3. The present legal status of Formosa and the Pescadores is that they are a portion of the Japanese Empire awaiting final disposition by a treaty of peace. The U.S. position regarding the status of the islands is qualified by the Cairo Declaration by the Chiefs of State of the U.S., U.K. and China and the policy which the U.S. has followed since V-J Day of facilitating and recognizing Chinese de facto control over the islands.
3. 福爾摩沙和澎湖目前的法律地位是：其為日本帝國的一部分，且正在等待通過和平條約進行最後處置。 美國關於該島嶼地位的立場符合美、英、中各國元首的《開羅宣言》以及美國自「對日戰爭勝利紀念日」以來所遵循的政策，即促進和承認中國對這些島事實上 的控制權。
[ source: United States Department of State / Foreign relations of the United States, 1949. The Far East: China, Volume IX (1949), page 271 ]
See -- FRUS page for full content
[中文版本] https://www.twdefense.info/trust3/frusch-1949av.htm