The United States and 12 allies issued what amounted to a final warning to Houthi rebels on Wednesday to cease their attacks on vessels in the Red Sea or face potential targeted military action.
The Yemen-based militants have carried out at least 23 attacks in response to the Israel-Hamas war in Gaza since December 19.
A senior Biden administration official declined to detail rules of possible engagement if the attacks continue, but underscored that the Iranian-backed Houthis should "not anticipate another warning" from the US and its allies.
The official, who spoke on the condition of anonymity under ground rules set by the White House, spoke soon after the countries issued a joint statement earlier on Wednesday condemning the attacks and underscoring that international patience was strained.
The statement was signed by the United States, Australia, Bahrain, Belgium, Canada, Denmark, Germany, Italy, Japan, Netherlands, New Zealand, Singapore and the United Kingdom.
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"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. "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."
For weeks, the Houthis have claimed attacks on ships in the Red Sea that they say are either linked to Israel or heading to Israeli ports. They say their attacks aim to end the Israeli air-and-ground offensive in the Gaza Strip that was triggered by the Palestinian militant group Hamas' October 7 attack in southern Israel.
However, the links to the ships targeted in the rebel assaults have grown more tenuous as the attacks continue.
The attacks have targeted commercial shipping vessels transiting through the critical Bab el-Mandeb Strait that links markets in Asia and Europe since the October 7 attack by Hamas and Israel's subsequent war against the militant group in Gaza.
The US and its allies have formed Operation Prosperity Guardian to protect ship traffic, and currently, warships from the United States, France and the United Kingdom are patrolling the area. On Sunday, US helicopters opened fire on Houthi rebels after they attacked a cargo ship in the Red Sea, killing several of them.
The US Navy helicopters returned fire in self-defence, sinking three of the four boats and killing the people on board while the fourth boat fled the area, the US Central Command said. The Houthis acknowledged that 10 of their fighters were killed in the confrontation and warned of consequences.
US ships in recent weeks have shot down waves of Houthi ballistic missiles and one-way explosive drones.
President Joe Biden has sought to keep the three-month war between Israel and Hamas from escalating into a broader regional conflict. But the official stressed that the US and its allies would respond similarly to such malign action that has impacts on global commerce anywhere around the globe.
The official said any potential action against the Houthis will be done in a "very smart way that does not potentially draw us in deep to a situation" with Iran and its proxy groups.
Biden last week ordered US airstrikes against Iranian-backed militia groups, including Kataib Hezbollah, after three US service members were injured in a drone attack in northern Iraq.
In November, US fighter jets struck a Kataib Hezbollah operations centre and command and control node, following a short-range ballistic missile attack on US forces at Al-Assad Air Base in western Iraq. Iranian-backed militias also carried out a drone attack at the same air base in October, causing minor injuries.
