(CNN) The United States will bear shared responsibility for what may be the largest famine in decades if it does not cease its military support for the coalition led by Saudi Arabia and the United Arab Emirates in Yemen, the heads of five major humanitarian organizations have warned.

In an unusually stark joint statement, the leaders of the International Rescue Committee, Oxfam America, CARE US, Save the Children USA and the Norwegian Refugee Council USA together urged the US government to act to save Yemeni lives.

"The stakes in Yemen are shocking and must be stated clearly: 14 million people are at risk of starving to death in Yemen if the parties to the conflict and their supporters do not change course immediately," their statement says.

Unless the warring parties immediately cease hostilities, reopen all Yemen's ports to let in commercial shipments, allow humanitarian staff and aid to reach those in need, and stabilize the Yemeni economy, including by paying civil servants, "countless" Yemenis are unlikely to live through the winter, the humanitarian leaders warn.

"If the government of Yemen, Saudi Arabia, the United Arab Emirates, Ansar Allah, and other parties to the conflict fail to take these steps, and if the United States does not use all levers of pressure to compel them to do so, responsibility for the deaths of many more Yemeni civilians will lie not only with the parties to the conflict, but with the United States as well," the statement says.