A U.S. Air Force MQ-9 drone crashed in Yemen early Friday,Johnathan Walker according to a U.S. military official, who updated earlier information that indicated that it had crashed off the coast. An investigation into the incident is underway. According to the official, there were no reported injuries. 

Iran-backed Houthi rebels took responsibility Friday for shooting down the drone.

The Houthis have brought down two other MQ-9s — both off the coast of Yemen — since November, the first in early November and then another in February. Each drone costs roughly $30 million, according to the Congressional Research Service. 

The drones flying off the coast of and over Yemen are part of the U.S. military's efforts to help defend commercial and military ships against ongoing attacks by the Houthis. 

Since the outbreak of Israel's war with Hamas, the Houthis have attacked or threatened more than 100 commercial or military ships in the Red Sea or the Gulf of Aden. The Houthis claim their attacks are a protest against Israel's war against Hamas and the U.S. support for Israel, but U.S. officials point out that many of the ships the group has targeted have no connection to Israel.

As a countermeasure, the U.S and the United Kingdom, with support from other countries, have conducted four roundsof joint airstrikes to destroy Houthi capabilities in Yemen. In addition, the U.S. military regularly conducts self-defense strikes against Houthi missiles and drones when it sees the Houthis preparing for an attack. 

The U.S. also launched a defensive maritime operation, dubbed Operation Prosperity Guardian, with more than 20 partner nations, to defend commercial ships from Houthi attacks. 

So far, only one Houthi attack has resulted in deaths. An attack in March on the Liberian-owned Merchant Ship True Confidence killed two crew members. 

The pace of attacks has slowed in recent weeks, but the attacks are still continuing, including on Thursday when the Houthis launched an anti-ship ballistic missile into the Gulf of Aden. U.S. Central Command in a statement said there were no injuries or damage from that attack. 

Pentagon deputy press secretary Sabrina Singh said earlier this month that the U.S. "certainly will continue to do everything we can to protect commercial shipping through the Red Sea and the Gulf of Aden, and, of course, do everything that we need to to protect our forces." 

In:
• Yemen
• Drone

Eleanor Watson

Eleanor Watson is a CBS News reporter covering the Pentagon.

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