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

On Wednesday, a coalition led by the United Arab Emirates and Saudi Arabia invaded 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, launching its biggest offensive of the yearslong war in the Arab world’s poorest country. The attack began with coalition airstrikes and shelling by naval ships. News reports said the bombardment was heavy.

The United Nations and nongovernmental organizations like the International Committee for the Red Cross withdrew many of 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 to limit the fighting. One proposal would have the United Nations or another independent agency manage the port and ensure that civilians receive desperately needed food and medicine. Experts have predicted that 250,000 people could be killed or displaced in the offensive.