Standing by. That’s about all the Trump administration has been doing as America’s allies on the Arabian Peninsula prepared to intensify Yemen’s misery.

A coalition led by the United Arab Emirates and Saudi Arabia is poised to attack the Red Sea port of Al Hudaydah, the home to 600,000 Yemenis and the lifeline for humanitarian aid that sustains most of the country’s people. Early Wednesday morning, there were reports that the battle for the port city had in fact begun.

The United Nations and nongovernmental organizations like the International Committee for the Red Cross withdrew their staffs as the attack on Iranian-backed Houthi rebels, who seized Al Hudaydah two years ago, looked increasingly certain.

Meanwhile, United Nations diplomats have worked urgently to prevent a full-scale offensive; now those efforts will be even more important to try and limit the fighting. One proposal would have the United Nations or another independent agency manage the port and ensure civilians receive desperately needed food and medicine. Experts have predicted that 250,000 people could be killed or displaced in the offensive.

Over the course of this conflict, President Trump has emboldened Saudi and emirati leaders. He shares their antipathy for Iran and will sell them virtually any weapon they want.

The Trump administration, which also supplies the coalition with intelligence, refueling capabilities and other assistance, has sent mixed signals about the Hudaydah offensive. While the Pentagon urged the coalition not to attack, a statement by Secretary of State Mike Pompeo on Monday made no such explicit request. Instead, he made clear to the emirate leaders “our desire to address their security concerns while preserving the free flow of humanitarian aid and lifesaving commercial imports.” He mildly called for all sides to work with the United Nations on a political solution.

The war began in 2014, when Houthi rebels and forces loyal to the ousted former president, Ali Abdullah Saleh, took control of the capital, Sana, and much of the rest of the country. In 2015, the Saudi-led coalition, with President Barack Obama’s backing, launched airstrikes against the Houthi forces.

The United Arab Emirates and Saudi Arabia, both Sunni Arab nations, see the Al Hudaydah offensive as a way to break a stalemate in the war and deal a crippling blow to the indigenous Houthis and their backers in Shiite-led Iran, which the Sunnis consider their chief rival for regional influence.

They have accused the Houthi rebels of using the port to smuggle in arms, including missiles, allegedly supplied by Iran to attack Saudi Arabia. A United Nations panel has expressed doubt that Al Hudaydah is a weapons transit point, and other experts question whether Iran provided the missiles.

Although coalition leaders have argued that the offensive can be carried out quickly, they have repeatedly miscalculated over the years, trapping their countries in a quagmire. The result has been countless civilian deaths, many attributed to indiscriminate coalition bombing attacks. Under international law, these attacks may qualify as war crimes in which the United States and Britain, another arms supplier, are complicit.

In all, more than 10,000 people have been killed in the war in Yemen, one of the world’s poorest countries and the battleground for a separate struggle by the United States and its regional allies against an affiliate of Al Qaeda. About 22 million Yemenis need humanitarian aid, and 8.4 million are at risk of starvation.

The Trump administration should speak with one voice to its Arab allies, making clear that an attack on Al Hudaydah will be a disaster and that even considering such action reveals how futile their policy in Yemen has been. Working with the Houthis and the United Nations on a cease-fire and a deal for neutral control of the port could be the first step to a political settlement that is the only hope for peace.

This editorial was updated.