Unless you're the United States PresidenTrump or the United States Secretary of State you'll need to provide an article or source for such information, for us to believe you, that is.
Pics...err facts or it didn't happen!
Seriously, where did you obtain this information?
If it's not yet decided in the courts than US citizens can continue to conduct business with Venezuelan exchanges until the point at which the US Courts declare such activity illegal.
A better question - what major crypto currency exchange operates out of Venezuela? Name one!
Unless somebody already posted the same, I'm guessing it came from here https://www.reddit.com/r/CryptoCurrency/comments/7zfp9p/this_needs_to_be_said_if_you_are_a_us_resident_or/.
Summer Wylie
Washington Post also issued a warning about Petros
https://www.washingtonpost.com/news/monkey-cage/wp/2018/02/26/bitcoin-move-over-theres-a-new-cryptocurrency-in-town-the-petro/?utm_term=.36dfa5f238c6