Some supporters of Taiwan independence argue that the language in the San Francisco Peace Treaty proves the notion that Taiwan is not a part of the Republic of China, for it does not explicitly state the sovereignty status of Taiwan after Japanese renunciation. In 1955, U.S. Secretary of State John Foster Dulles, co-author of the San Francisco Peace Treaty, affirmed that the treaty ceded Taiwan to no one; that Japan "merely renounced sovereignty over Taiwan". Dulles said that America "cannot, therefore, admit that the disposition of Taiwan is merely an internal problem of China." This legal justification is rejected by both the PRC and ROC governments, both of which base their legal claims on Taiwan on the Instrument of Surrender of Japan which accepts the Potsdam Declaration and the Cairo Declaration. However, the treaty specifies that Japan renounced its sovereignty over Taiwan effective April 28, 1952; there is no recognition that there was any transfer of Taiwan's territorial sovereignty to any party before this date. In more recent years supporters of Taiwan independence have more often relied on arguments based on self-determination as implied in the San Francisco Peace Treaty and popular sovereignty, but the United Nations has consistently rejected such arguments.