"I am both saddened and frustrated to know that we have been in a position to help ease the suffering of hundreds of thousands of people and help mitigate further loss of life, but have been unable to do so because of the unrelenting position of the Burma military junta," Admiral Timothy Keating, the military's top commander in the Pacific, said in a statement Wednesday.
Keating said the U.S. made 15 unsuccessful attempts to convince Myanmar's military government to accept the aid.
In a statement Wednesday, White House press secretary Dana Perino said the U.S. ships had been "immediately deployed to Burma in the spirit of goodwill to offer extensive and life-saving assistance to the victims of Cyclone Nargis. Tragically, the Burmese authorities refused to accept this assistance."
The announcement comes one month after the cyclone devastated the country, leaving at least 78,000 people dead and 56,000 missing.
On Tuesday, the United Nations released its latest, bleak, assessment of the situation for the storm's 2.4 million survivors.
Aid groups have been unable to reach 1.1 million people, and of the 1.3 million who are getting some help, most have received "inconsistent levels of assistance," the report said.
"There remains a serious lack of sufficient and sustained humanitarian assistance for the affected populations," the U.N. reported.
The Associated Press reports that it has interviewed survivors in recent days who have not received any help from the government, and are going without food and being forced to drink from dirty canals.
One of the biggest obstacles for aid groups has been reaching the hard-hit delta region. Normally, in large-scale disasters, groups would use military helicopters to fly in food, water and supplies, U.N. World Food Programme Spokesman Paul Risley told the AP.
The aid delivery difficulties come despite U.N. chief Ban Ki-moon's trip to Myanmar in late May to meet with the country's military government -- including top leader Senior Gen. Than Shwe -- during which the junta agreed to allow "all aid workers" into the cyclone-ravaged country.
But Myanmar has refused military helicopters from the U.S. and other countries. The government has provided the WFP with only seven helicopters, according to Risley. The organization has chartered 10 more private helicopters. It is aiming to raise $70 million to fund the operation, but so far is 64 percent short, according to the AP.
Keating said that the U.S. will leave several helicopters in Thailand.
"Should the Burmese rulers have a change of heart and request our full assistance for their suffering, we are prepared to help," he said.