I’m not sure what Russia’s options are here, beyond creating hazards to navigation. They certainly can’t fire on a foreign flagged ship. The P-8 they have monitoring it is signaling that the US is potentially prepared to respond in real time. In addition, attacking a foreign-flagged civilian vessel, especially one so clearly identified, would be a very dangerous gambit with a low payoff and potentially lethally high cost. It’s not even the Israelis. It’s that the world might become involved if it’s the straw that broke the camel’s back about Russia being a rogue nation that needs to be contained before the conflagration spreads.

I don’t even think they can mine the harbor at this point. That ship sailed, no pun intended. Mining the harbor at this point could be interpreted as an attack on this vessel.

If they can present a physical blockade such that the Israeli shipment (the ship is not Israeli flagged btw, but that’s not unusual), they might be able to do it. That’s easier said than done, because they’d have to do so at sea out of range of Ukrainian weapon systems.