PORT-AU-PRINCE, Haiti – Relief workers began handing out women-only food coupons, launching a new phase of what they hope will be less cutthroat aid distribution to ensure that families and the weak get supplies following Haiti's devastating earthquake.

Young men often force their way to the front of aid delivery lines or steal from it from others, meaning aid doesn't reach the neediest at rough-and-tumble distribution centers, according to aid groups.

The World Food Program coupons can be turned in by women at 16 sites in the capital starting Sunday, and entitle each family to 25 kilograms (55 pounds) of rice.

U.N. officials say they are still far short of reaching all 2 million quake victims estimated to need food aid.

Meanwhile, federal agencies scrambled to explain the U.S. military's suspension of medical evacuations of critically ill Haitians to the United States in a dispute over where the victims should be treated.

"We have 100 critically ill patients who will die in the next day or two if we don't Medevac them," said Dr. Barth Green, chairman of the University of Miami's Global Institute for Community Health and Development. That included 5-year-old Betina Joseph, who developed tetanus from a small cut in her thigh. Doctors said Saturday that she had just 24 hours to live if not provided with respirator care.

White House officials said they were working to increase hospital capacity in Haiti and aboard the USNS Comfort hospital ship as well as in the United States. U.S. Ambassador to Haiti Kenneth Merten said about 435 earthquake victims had been evacuated before the suspension, and that he was "sure the Department of Defense wants to do the right thing."

Relief officials were facing a growing sanitation crisis that could spread malaria, cholera and other deadly diseases throughout the chaotic camps.

Shortages of food, clean water, adequate shelter and latrines are creating a potential spawning ground for epidemics in a country with an estimated 1 million people made homeless by the Jan. 12 quake.

In one camp, a single portable toilet served about 2,000 people, forcing most to use a gutter that runs next to an area where vendors cook food and mothers struggle to bathe their children.

Survivors have erected flimsy shelters of cloth, cardboard or plastic in nearly every open space left in the capital.

Women wait until night to bathe out of buckets, shielding their bodies behind damaged cars and trucks. Water is recycled — used first for brushing teeth, then for washing food, then for bathing.

"My 1-year-old has had diarrhea for a week now, probably because of the water," said Bernadel Perkington, 40. "When the earthquake happened I had 500 gourdes (about 15 U.S. dollars), which I was using for clean water for her. The money for that ran out yesterday."

The crowding and puddles of filthy water that breed mosquitoes have begun to spread diseases such as dengue and malaria, which were already endemic in Haiti. Some hospitals report that half the children they treat have malaria, though the rainy season — the peak time for mosquitoes — won't start until April.

Tight quarters also expose people to cholera, dysentery, tetanus and other diseases.

The U.N., Oxfam and other aid organizations have started to dig latrines for 20,000 people, said Silvia Gaya, UNICEF's coordinator for water and sanitation, even if that's a small fraction of the 700,000 people that officials said were living in the camps last week.

"In some parks, there is no physical space" even to dig latrines, Gaya said.