The U.S. Navy boarded a ship in the Red Sea suspected of running weapons to rebel forces in Yemen. The Wall Street Journal reported the boarding was the first active role the U.S. has taken in the current Yemeni uprising. U.S. officials are wary Iranian influence could sway the war in the rebels' favor.

The U.S. fears Iranian intervention in the rebellion would directly affect Saudi Arabian allies. The Saudis are leading the airstrikes against the rebels currently occupying much of Yemen. Iranian supplies of surface-to-air missiles would prove disastrous to the current operation. Senior defense officials say they are certain Iran has been a longtime supplier to the Houthi movement.

Two weeks ago, Houthi rebels and military forces forced current President Abed Rabbo Mansour Hadi to flee the country. The Saudi-led airstrikes that began in March have claimed hundreds of lives and displaced tens of thousands. Tehran has called for an end to the airstrikes as U.S. and Saudi forces have sided with Hadi. The U.S. announced it will also contribute to the war effort.

“We know they are trying to do it,” said a senior U.S. defense official about Tehran’s campaign. Another senior official told the Journal the Iranians are not really invested in the Houthis' success, but if the risk of helping the rebels is low, Tehran likely will take the chance. Iran reportedly has sent members of its elite guard to Yemen to train rebels, but Iran has vehemently denied it has run supplies to the Houthis.  

U.S. forces have been placed on alert in the Red Sea area and are stepping up surveillance efforts. There are currently more than a dozen countries with warships in those waters, including Iran, reportedly with two. The strategy for U.S. and Saudi fighters is to destroy the supply chains Iran has been using. Airstrikes have erased runways, and it is hoped extra eyes on the seas will deter further Iranian intervention.