A week after the Trump administration abruptly ordered a sweeping halt to U.S. foreign development aid, the effect is already being felt in war-torn Ukraine. Several humanitarian organizations say they have been forced to suspend operations, including assistance to war veterans and internally displaced people.

The orders, which were issued while the Trump administration conducts a 90-day audit of foreign aid, have sent a chill through humanitarian organizations in Ukraine, which depend heavily on such assistance.

The United States, the largest single source of aid to Ukraine, has provided more than $37 billion in humanitarian aid, development assistance and direct budget support since the beginning of the war nearly three years ago through its Agency for International Development, also known as U.S.A.I.D.

Yuriy Boyechko, the founder and chief executive of Hope for Ukraine, which works with U.S.-funded Ukrainian groups to supply firewood to frontline residents, said the impact of the halt in funding would be immediate. Deliveries will stop suddenly, he said, leaving people on their own in the middle of winter.

“They’re going to feel the effect of this next week,” Mr. Boyechko said in an interview. “This is just extremely harmful because you have millions of people in frontline areas near Kherson and Kharkiv who have been living without light for a long time. For them, firewood has been the only source of heat and a way to prepare food.”

Ivona Kostyna, chairwoman of Veteran Hub, an organization that supports veterans and their families, said that the organization had already stopped two major programs: one that liaises with Ukrainian employers on employment policies for veterans, and another that provides space for veterans.