WASHINGTON (AP) — The United States and 12 allies issued a final warning of sorts Wednesday to Houthi rebels to stop their attacks on ships in the Red Sea or face targeted military action.

Yemen-based militants have carried out at least 23 attacks since December 19 in response to the war between Israel and Hamas in Gaza.

A senior Biden administration official declined to detail the rules for possible engagement if the attacks continue, but stressed that the Iran-backed Houthis should expect “no further warning” from the US and its allies.

The official, who spoke on condition of anonymity in line with ground rules set by the White House, spoke shortly after the countries issued a joint statement earlier Wednesday condemning the attacks and stressing that international patience was strained.

The declaration was signed by the United States, Australia, Bahrain, Belgium, Canada, Denmark, Germany, Italy, Japan, the Netherlands, New Zealand, Singapore and the United Kingdom. Separately, the US on Wednesday called on the United Nations Security Council to take action against the Houthis and warned their financier Iran that it must make a decision to continue supporting the rebels.

“Let our message now be clear: we demand an immediate end to these illegal attacks and the release of the illegally detained vessels and crew,” the countries said. “The Houthis will bear responsibility for the consequences if they continue to threaten lives, the global economy and the free flow of trade in the region’s vital waterways.”

For weeks, the Houthis have claimed attacks on ships in the Red Sea that they believe are either connected to Israel or bound for Israeli ports. They say their attacks are aimed at ending Israel’s air and ground offensive in the Gaza Strip, which was triggered by the Palestinian militant group Hamas’ October 7 attack in southern Israel.

However, the connections to the target ships of the rebel attacks become increasingly weaker the longer the attacks last.

The attacks targeted merchant ships passing through the critical Bab el-Mandeb Strait, which connects markets in Asia and Europe, since Hamas’ Oct. 7 attack and Israel’s subsequent war against the militant group in Gaza.

The US and its allies have formed Operation Prosperity Guardian to protect shipping traffic, and warships from the US, France and the UK are currently 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.

According to U.S. Central Command, U.S. Navy helicopters returned fire in self-defense, sinking three of the four boats and killing those on board, while the fourth boat fled the area. The Houthis admitted that 10 of their fighters were killed in the confrontation and warned of the consequences.

U.S. ships have shot down waves of Houthi ballistic missiles and one-way explosive drones in recent weeks.

President Joe Biden has sought to prevent the three-month war between Israel and Hamas from escalating into a larger regional conflict. However, the official stressed that the U.S. and its allies would respond similarly to such malign actions that impact global trade around the world.

“As the president has made clear, the United States does not seek conflict with any nation or actor in the Middle East, nor do we want the war between Israel and Hamas to expand in the region,” said National spokesman John White House Security Council Kirby said. “But we will not shy away from the task of defending ourselves, our interests, our partners or the free flow of international trade.”

The official said any possible action against the Houthis will be carried out in a “very smart way that may not drag us into a situation” with Iran and its proxy groups.

At the United Nations, U.S. Deputy Ambassador Christopher Lu said that without Iranian support, the Houthis would have “difficulty effectively detecting and attacking commercial vessels navigating shipping routes through the Red Sea and Gulf of Aden.”

Biden last week ordered U.S. airstrikes against Iran-backed militia groups including Kataib Hezbollah after three U.S. soldiers were injured in a drone strike in northern Iraq.

In November, US fighter jets attacked a Hezbollah operations center and command and control node in Kataib after a short-range missile attack on US forces at Al-Asad air base in western Iraq. Iran-backed militias also carried out a drone strike on the same air base in October, resulting in minor injuries.

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Associated Press reporter Edith M. Lederer contributed from the United Nations.