January 26, 1963
DURING the present discussions in Washington and New York on the nuclear test ban treaty among the Soviet Union, the United Kingdom, and the United States, I have asked the Atomic Energy Commission to postpone underground shots in Nevada. We are maintaining the capability and readiness to resume our test program at any time. We have no intention of again accepting an indefinite moratorium on testing, and if it is clear we cannot achieve a workable agreement we will act accordingly.
John F. Kennedy, Statement by the President on Postponing Underground Testing in Nevada. Online by Gerhard Peters and John T. Woolley, The American Presidency Project https://www.presidency.ucsb.edu/node/236258