Despite the severity of the situation, the government has retreated into angry denial rather than seek urgent assistance. Mr. Maduro lashed out at President Trump, telling him to “Get your pig hands out of here.” And Foreign Minister Delcy Rodríguez recently derided the notion of humanitarian assistance as “a theory constructed by the Pentagon so that the U.S. can intervene.”

Even worse, when aid has nonetheless arrived in the country, it has been regularly confiscated by the military or police before it could be delivered to the people.

The world isn’t even close to being ready to respond at the scale required, even if access was available. This must be remedied — and fast. First, the United Nations Secretary-General, António Guterres, should appoint a humanitarian coordinator to oversee preparations for assisting the people of Venezuela and begin mobilizing financial and other support from donors. Second, the United Nations should publicly insist on being given access to Venezuela to conduct a comprehensive assessment of its needs. And finally, the international community must demand that Mr. Maduro not only allow assistance to enter Venezuela, but that it be distributed exclusively by reputable international organizations on the basis of need.

While aid cannot be provided forcibly without Mr. Maduro’s assent as long as he maintains effective control over Venezuela’s borders, the world must develop and be prepared to execute a major relief operation the moment permission is granted or otherwise becomes possible.

Furthermore, in 2005 the United Nations adopted the doctrine of the “responsibility to protect,” which built on existing international legal obligations of states to reaffirm that each state’s sovereignty carries a duty to protect its citizens from mass atrocities, including crimes against humanity — and that if a state is committing atrocities, the international community must respond, through action by the Security Council if necessary. By his policy choices, Mr. Maduro has created and is dramatically magnifying the enormous human tragedy in Venezuela. This conduct constitutes a prima facie case of crimes against humanity under the category of “other inhumane acts” that intentionally cause great suffering or death.