M/V Helt Photo by Peter aus Holtenau via Marine Traffic
gCaptain reports that a NATO (Estonian) flag merchant vessel has been sunk, reportedly as a result of Russian action.
It was a small ship with a small crew. Two crewmembers were rescued. Four crewmembers are missing.
The circumstances of the loss were not clear. It may be that the ship was forced to transit a minefield.
Chuck Hill's CG Blog 
The was a article in “gCaptain” where the Russians were secretly “Mining” Ukrainian waters…
( https://gcaptain.com/russia-may-have-mined-ukrainian-waters-says-nato/?subscriber=true&goal=0_f50174ef03-b032197207-169896457&mc_cid=b032197207&mc_eid=dcde600992 )
This report indicates the ship was at anchor when it experienced an explosion, presumably from a mine. https://www.navalnews.com/naval-news/2022/03/estonian-cargo-ship-sinks-off-the-coast-of-odessa/