Tit for tat by Iran in response to the American shadowing of the Iranian flotilla off of Yemen?
A Marshall Island flagged vessel, last port of call Jeddah.
This may not focus on the US.
http://www.marinetraffic.com/en/ais/details/ships/shipid:1635726/mmsi:538005749/imo:9694581/vessel:MAERSK_TIGRIS