[jdsteel]

“ What exactly is the legal basis for the U.S. to intercept foreign vessels like this in international waters?”

Our sanctions against those nations, of which we have made the world very clear.

[Alberta's Child]

The U.S. can impose sanctions against foreign countries at will. We've done that with both Iran and Venezuela. These sanctions apply to trade with the U.S.

The U.S. has no legal or moral right to use military means constrain trade among other nations that are not at war with the U.S.