This hasn't hit major news wires yet, but it looks real according to Al Arabiya's twitter feed:
https://twitter.com/alarabiya_brk
Arab urgently @ AlArabiya_Brk · 3m 3 minutes ago
Iran fired on a US cargo ship and Taktefha to the port of Bandar Abbas # Arabah_aajl
Arab urgently @ AlArabiya_Brk · 9m 9 minutes ago
Photos directly to artillery shelling on the Yemeni border with Saudi Arabia #
Arab urgently @ AlArabiya_Brk · 12m 12 minutes ago
American held by Iran ship includes 34 American sailors # Arabah_aajl
Iran seizes power on a US cargo ship and Tguetadha to the port of Bandar Abbas # Arabah_aajl
Update, some major news orgs starting to relay the info:
http://www.huffingtonpost.com/2015/0...n_7161152.html
http://uk.reuters.com/article/2015/0...0NJ1QZ20150428
http://www.bbc.com/news/world-middle-east-32503660
Cue the conspiracy theories, see page 39:
http://www.brookings.edu/~/media/res...n_strategy.pdf