The U.S has deployed warships to Yemen to survey any ship leaving Iran that could be suspected for illegally moving guns to Houthi rebels. The U.S doesn't however has direct authority to board Iran flagged ships. This is probably due to that earlier in the month the U.S boarded a Panamanian ship that was suspected of trafficking people, drugs, and guns but nothing was found. However, the U.S may board Iranian ships if they proceed into Yemen waters. “U.S. warships from the carrier group of the USS Theodore Roosevelt are joining allied vessels from Saudi Arabia, Egypt and other partner nations prepared to intercept a convoy of 7-9 Iranian vessels believed headed for Yemen.” said Jim. The U.S hope to catch many ships transporting guns illegally.
Sciutto, Jim. "U.S. Warships to Monitor Ships Traveling from Iran - CNN.com." CNN. Cable News Network. 20 April. 2015. Web. 21 April. 2015. http://www.cnn.com/2015/04/20/politics/iran-united-states-warships-monitoring/index.html