Vice Admiral Brad Cooper, the head of US Navy operations in the Middle East, said it was the first time the Houthis had used an unmanned surface vessel, or USV, since their harassment of commercial ships in the Red Sea began after the outbreak of the Israel-Hamas war.
An armed unmanned surface vessel launched from Houthi-controlled Yemen got within a "couple of miles" of US Navy and commercial vessels in the Red Sea before detonating on Thursday, just hours after the White House and a host of partner nations issued a "final warning" to the Iran-backed militia group to cease the attacks or face potential military action.
Vice Admiral Brad Cooper, the head of US Navy operations in the Middle East, said it was the first time the Houthis had used an unmanned surface vessel, or USV, since their harassment of commercial ships in the Red Sea began after the outbreak of the Israel-Hamas war. They have, however, used them in years past.
Fabian Hinz, a missile expert and research fellow at the International Institute for Strategic Studies, said the USVs are a key part of the Houthi maritime arsenal and were used during previous battles against the Saudi coalition forces that intervened in Yemen's war. They have regularly been used as suicide drone boats that explode upon impact.
Most of the Houthis' USVs are likely assembled in Yemen but often fitted with components made in Iran, such as computerised guidance systems, Hinz said.
At the United Nations, US deputy ambassador Christopher Lu said at a emergency Security Council meeting on Wednesday that Iran has supplied the Houthis with money and advanced weapons systems, including drones, land attack cruise missiles and ballistic missiles. He said Iran also has been deeply involved in planning the Houthis' attacks on commercial vessels in the Red Sea.
He said the United States is not seeking a confrontation with Iran, but Tehran has a choice.
"It can continue its current course," Lu said, "or it can withhold its support without which the Houthis would struggle to effectively track and strike commercial vessels navigating shipping lanes through the Red Sea and Gulf of Aden".
This raises questions as to whether any action against the Houthis would also address Iran's role in any way, which could risk widening the conflict.
A statement on Wednesday signed by the United States, Australia, Bahrain, Belgium, Canada, Denmark, Germany, Italy, Japan, Netherlands, New Zealand, Singapore and the United Kingdom gave the Houthis what a senior Biden administration official described as a final warning.
"Let our message now be clear: we call for the immediate end of these illegal attacks and release of unlawfully detained vessels and crews," the countries said in the statement. "The Houthis will bear the responsibility of the consequences should they continue to threaten lives, the global economy, and free flow of commerce in the region's critical waterways."
Since late October, the Houthis have launched scores of one-way attack drones and missiles at commercial vessels transiting the Red Sea. US Navy warships have also intercepted ballistic missiles the Pentagon says were headed toward Israel. Cooper said a total of 61 missiles and drones have been shot down by US warships.
In response to the Houthi attacks, Defence Secretary Lloyd Austin in December announced Operation Prosperity Guardian, with the United States and other countries sending additional ships to the southern Red Sea to provide protection for commercial vessels passing through the critical Bab el-Mandeb Strait.
Cooper said 1,500 commercial ships have been able to transit safely since the operation was launched on December 18.
However, the Houthis have continued to launch missiles and attack drones, prompting the White House and 12 allies to issue what amounted to a final warning on Wednesday to cease their attacks on vessels in the Red Sea or face potential targeted military action.
Cooper said Operation Prosperity Guardian was solely defensive in nature and separate from any military action the US might take if the Houthi attacks continue.
The US, the United Kingdom and France are providing most of the warships now, and Greece and Denmark will also be providing vessels, he said.