Nearly a month after the storm tore through Myanmar, about 60 per cent of the 2.4 million survivors remain without foreign aid, despite some opening up by the military rulers after an intense UN-led diplomatic push.
The junta blocked entry to overseas aid workers in the critical days after Cyclone Nargis pummelled the impoverished nation on May 2-3, leaving 133,000 people dead or missing.
"Unless the regime changes its approach, its policy, more people will die," Gates said while travelling to Bangkok after a regional security forum in Singapore.
"I would describe it as criminal neglect."
Gates, who earlier said Myanmar's initial delays could have cost tens of thousands of lives, said the United States would decide within days whether to recall four US Navy ships waiting to deliver aid.
He said it was "becoming pretty clear" the junta would not accept military help from the United States, which has been a fierce critic of the regime.
The USS Essex and three other ships have been off the coast of Myanmar for more than two weeks with a dozen helicopters, landing craft and Marines, but have been refused permission to use them to distribute relief.
Malaysia's deputy prime minister Najib Razak, speaking at the same forum in Singapore that Gates attended, urged the regime to accept military helicopters and rubber boats from its Southeast Asian neighbours.
"The only organisation that can be effective in terms of disaster relief operations is the military," Najib told reporters.
"There is a huge human tragedy of the highest proportion that might befall the people of Myanmar if the government does not allow greater participation by the [Southeast Asian] countries and by the world," Najib added.
Supplies are slowly trickling through to worst-hit areas, but the generals – notoriously suspicious of the West – are wary of what is coming in.
"We would warmly welcome any assistance and aid that are provided with genuine goodwill from any country or organisation, provided there are no strings attached, or politicisation involved," Deputy Defence Minister Aye Myint said in Singapore.
That stance earned Aye Myint "a good old-fashioned ear-bashing" from donor nations represented at the conference, Canadian Defence Minister Peter MacKay told AFP, adding Myanmar appeared to be in "a state of denial."
MacKay said Canada and other nations have been ready to supply food, water, clothing, shelter and other basics, but "have met with considerable reticence and reluctance to let that relief flow."
While more foreign aid workers are now being allowed into Myanmar, they are still finding it difficult to gain access to some of the hardest-hit areas – where villagers say they have received little or no government help.
What they are finding instead is that many people remain without clean water or shelter, and are at risk of disease.
With the monsoon rains now hitting hard, survivors are at increased risk of respiratory infections, aid group Doctors Without Borders said in a statement.
Residents in the Irrawaddy Delta village of Kanzeik are only now getting the plastic sheets and clean water that should have arrived long ago.
"I was so happy once I saw the aid boat entering the village," said Kyaw, a 35-year-old with four children.
"I'm so glad that I got what I really need for my family now. At least our family can live safely under the rain for this year," he told AFP.
With crucial supplies now arriving, aid groups hope storm victims can think about returning to the fields in this key rice-growing area – but many others in need of food, shelter and medicine still remain out of reach.
Aye Win, the UN's spokesman in Yangon, said about 41 per cent of survivors, or close to one million people, had received some form of assistance.
"There have been some improvements" in access and visas, he said, "albeit not as much as we would like".