Upvote:2
The Cuba sanctions are under 31 CFR § 515 and the relevant part is:
Well, are you subject to U.S. jurisdiction?
(b) Any person within the United States as defined in § 515.330;
31 CFR § 515.330 - Person within the United States
(1) Any person, wheresoever located, who is a resident of the United States;
(2) Any person actually within the United States;
That's crystal clear. The restrictions apply not only to citizens and residents but to anyone within the US. And the restrictions (first link) do not recognize a layover as a valid activity.