(CNN) -- U.S. Navy ships loaded with supplies for victims of Myanmar's cyclone will sail away from the country's coast on Thursday, after the ruling junta refused for three weeks to allow them to deliver aid.
U.S. ships steam in formation off the coast of Myanmar on May 23.
Adm. Timothy Keating said the USS Essex group would leave the shores of Myanmar, also known as Burma, on Thursday, but that he would leave several heavy lift aircraft in Thailand to assist international relief efforts.
"We have made at least 15 attempts to convince the Burmese government to allow our ships, helicopters and landing craft to provide additional disaster relief for the people of Burma, but they have refused us each and every time," Keating said in a statement Wednesday.
Cyclone Nargis made landfall early last month, killing more than 77,000 people in the southeastern Asian country, according to a United Nations estimate.
Some 55,000 others are missing, the United Nations said, and as many as 500,000 to 600,000 people, mainly in the Irrawaddy Delta region, have had to be relocated.
The White House issued a statement Wednesday saying more than a million victims have yet to receive assistance. Watch a discussion of Myanmar's handling of the crisis »
"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," Keating said.
Myanmar leaders did grant permission for U.S. planes to deliver aid, a total of 106 plane-loads of supplies worth more than $26 million. Transportation cost about $6.8 million, it said.
But the junta never gave permission for the United States to distribute the aid directly to the storm victims, prompting questions about whether some of the assistance went astray.
Last weekend, U.N. Secretary-General Ban Ki-moon guided a conference of 52 donor nations in Myanmar, where countries pledged in excess of $100 million to help Myanmar recover -- and said they are willing to open up their wallets further once aid groups are granted access to the worst-affected areas.
The country's government had asked for $11 billion in assistance, saying that the relief phase of the disaster was already over and that it needed the money for reconstruction and rehabilitation efforts.
More than a month after the cyclone struck, more than 1 million people affected have received help, Elisabeth Byrs of the U.N. Office for the Coordination of Humanitarian Affairs said on Tuesday. She added that aid has reached nearly half of the people in the Irrawaddy Delta.
However, she said, "There remains a serious lack of sufficient and sustained humanitarian assistance."
On Tuesday, State Department spokesman Sean McCormack said that the United States would continue to push to get emergency supplies to the country's victims.
"We are not going to abandon those ... people," McCormack said. Of the Navy ships leaving the area, he said, they "are needed elsewhere and there is no rational expectation at this point we will be effectively able to use those assets in an humanitarian relief operation."
"Our folks will do the forensics on that to see if there are any lessons learned," McCormack said. "We think that to the extent that there has been significant loss of life that we as well as others could have reduced that number had we been allowed to act more quickly with a large-scale intervention."
CNN's Charley Keyes and Barbara Starr contributed to this report.