U.S. Navy ships laden with relief supplies steamed away from Myanmar's coast Thursday, their helicopters barred by the ruling junta though millions of cyclone survivors need food, shelter or medical care, a Navy spokesman said. The USS Essex group, which includes four ships, 22 helicopters and 5,000 U.S. military personnel, had been positioned off the Myanmar coast for more than three weeks hoping for a green light to deliver aid to the survivors. "The ruling military junta in Burma have done nothing to convince us that they intend to reverse their deliberate decision to deny much needed aid to the people of Burma. Based on this, the decision was made to continue with previous operational commitments," Lt. Denver Applehans said in an e-mail from the flotilla.

More than a month after the storm, many people in stricken areas still have received no aid at all and the military regime continued to impose constraints on international rescue efforts, humanitarian groups said Wednesday.

"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," said Adm. Timothy J. Keating, head of the U.S. Pacific Command. Myanmar is also known as Burma.

The USS Essex and three other amphibious assault ships, which have been in international waters off Myanmar since May 13, were ordered to resume their previously scheduled missions on Thursday, Keating said in a statement issued by his headquarters in Hawaii.

Keating said the U.S. had made "at least 15 attempts" to convince the junta to allow the ships to deliver aid directly to victims in the country's most badly damaged areas.

Help from French and British naval ships which had similarly broken off from their missions to stand by off Myanmar was also rejected.

The U.S. was allowed by the junta to fly in relief supplies to Yangon, the country's biggest city, and the flights by U.S. Marine Corps C-130s temporarily based in Thailand are continuing.

A total of 1.3 million survivors have been reached with assistance by local and international humanitarian groups, the Red Cross and the U.N., said the U.N's Office for the Coordination of Humanitarian Affairs, or OCHA.

"There remains a serious lack of sufficient and sustained humanitarian assistance for the affected populations," warned OCHA. The government says 78,000 people were killed by the cyclone and another 56,000 remain unaccounted for.

The junta, which explicitly rejected the use of foreign military helicopters in the relief effort, still has not authorized the entry of nine civilian helicopters flying on behalf of the U.N. World Food Program, though they have been sitting in neighboring Thailand since last week.

Restrictions on visa and travel permission for foreign workers, as well as on entry of some equipment, continue to hamper the aid effort, despite a pledge made almost two weeks ago by junta leader Senior Gen. Than Shwe to U.N. Secretary Ban Ki-moon to allow foreign aid workers free access to devastated areas.

"The small number of visas and the short duration of travel permits for access" into the delta area "continue to impose serious constraints on the effectiveness of overall operations," the International Federation of Red Cross and Red Crescent Societies said.

Despite the problems, the World Health Organization reported some cause for optimism.

In a report circulated Wednesday, it cited an assessment by the U.N. Children's Fund - UNICEF - of conditions in hard-to-reach areas outside of the town of Bogalay, one of the areas worst affected by the storm.

It quoted the assessment as saying "there were no post-cyclone deaths in any of the villages assessed," as well as no signs of acute malnutrition. It also said suitable sources were found for clean water.

The findings appeared to contradict fears that there would be a "second wave" of deaths after the cyclone due to the lack of immediate large scale assistance.

However, the French aid agency Doctors Without Borders warned Wednesday that as seasonal monsoon rains become heavier, there will be more challenges supplying aid and maintaining the good health of survivors.