War crimes require an armed conflict but not a "war". Note that declerations of war no longer really have meaning in international law and dont affect anything whether they are given or not.

Armed conflict can be either international (e.g. between two countries) or non-international (e.g. you are atacking a non-state group. For example ISIS. However note that attacking a non-state group on the territory of a different state without permission of that state makes it be both.). War crimes apply to both types but the rules are slightly different between the two.

Keep in mind also that people often colloquial use "war crimes" to mean any international crime, but technically its only one type. Crimes against humanity and genocide are technically not war crimes but a different category. They generally do not require an armed conflict (although often when they do happen its related to sone sort of armed conflict)

Anyways this whole thing probably counts an armed conflict. I think at the least its a non-international armed conflict with the drug cartel. Attacking boats is usually an act of war even if they are in international waters, which might make it an international armed conflict with venuzula as well if the boats are connected to it (but the rules related to that im not really clear on and is a bit beyond my knoeledge).

[IANAL]

The possibility of this being an ‘act of war’ does seem very interesting, but I’m not sure Venezuela could claim it in this circumstance, as the vessels do not appear to be ‘flagged’. I would be interested to learn what the status of unflagged vessels is in international law, and I suspect there must be law on the subject, as pirates were typically unflagged.