Donors and aid groups are planning to suspend humanitarian aid to Yemeni areas under the control of Houthis in the coming months if the group does not stop hindering the delivery of assistance, a senior US State Department official said on Tuesday.

Houthis in northern Yemen were obstructing efforts to get food and other help to those in need, to an extent that was no longer tolerable, and that operations would be scaled down, aid agency sources told Reuters earlier.

Speaking on condition of anonymity, the senior US State Department official confirmed those plans.

“Each donor and implementer is drawing up plans on how to, what to do if the Houthis do not change their behavior on the ground,” the official said. “The plans involve suspending a lot of assistance programs with exceptions for truly lifesaving programs feeding sick children and things like that.”

“Everyone’s looking at a timeline of a month or two. ... That’s the point at which different implementers will start to suspend some of the programs,” he said.

The United Nations describes Yemen as the world’s biggest humanitarian crisis and says millions of people are on the verge of starvation.

Aid agencies have for the past year publicly and privately complained of worsening operating conditions, lack of travel permits and other access restrictions.

The US Agency for International Development (USAID), a major donor, said it was extremely concerned that the Houthis had worsened the effects of the crisis by interfering in aid operations.

“We are urgently working on a way forward that allows US aid to continue uninterrupted, but are taking steps to plan ahead with our partners so they can safely and responsibly adjust programming should we be forced to reduce aid,” said acting USAID spokesperson Pooja Jhunjhunwala.