ABC News’ Kirit Radia reports: A top U.S. diplomat who traveled to Darfur last week is warning of a critical shortage of aid in refugee camps there. Alberto Fernandez, the top U.S. diplomat in Khartoum, traveled to El Fasher in North Darfur and to the Zam Zam Internally Displaced Person (IDP) camp to assess the impact of Sudan’s expulsion of 13 major aid groups that operated in the region. What he found was an aid gap that threatens the health and lives of hundreds of thousands of people. "While the United Nations and remaining NGOs are exploring ways to provide certain life-saving assistance, they would be unable to fill the gap created by this emergency," the State Department said last night in a written readout of Fernandez’s trip. Coupled with a recent arrival of 36,000 refugees fleeing recent fighting, the camps are overflowing with needy people that lack food and health care that were once provided by the aid groups. The State Department said the influx "has severely strained Zam Zam camp’s limited resources" and that the situation has been "exacerbated" by the aid groups’ expulsion. "There is a growing water shortage due to demand created by the recent IDP arrivals and the lack of available water resources at the camp. In addition, the influx of new IDPs has created a need for more land to accommodate the overflow," the State Department said. Similarly, some of the groups that were kicked out of the country earlier this month are warning of an impending humanitarian crisis. Oxfam, whose British team was asked to leave the country, said in a statement today that, "Already, some of the locations in Darfur where we used to work – such as Kalma camp home of over 88,000 people in South Darfur – are facing severe shortages of clean water. Only hand pumps are functioning and thousands of women are queuing for hours to get their tiny ration of water. There is also a critical lack of sanitation which increases risks by the day of serious outbreaks of diseases such as cholera and diarrhea." "Current stop-gap measures will only be effective for a short time," Oxfam warns. "As the rainy season arrives within the next two months, people living in weak temporary shelters, in flood-prone locations where latrines can fill and overflow, will become at extreme risk of disease and death. With the humanitarian capacity reduced by nearly 50%, responding to such emergency scenarios will be an enormous challenge for others to tackle." The heated rhetoric between Washington and Khartoum has intensified since Sudan’s President Omar al-Bashir announced he would expel the foreign aid groups, in apparent retaliation of a warrant issued for his arrest by the International Criminal Court for alleged war crimes committed in Darfur. Secretary of State Hillary Clinton has said Bashir would be personally responsible for every single death that resulted from his decisions. The State Department says it is engaged in intense diplomacy to try and convince Bashir to reverse his decision. Bashir later threatened to expel foreign ambassadors who he felt were overstepping their bounds.