YANGON, Myanmar (AP) — The U.S. military today ordered navy ships loaded with relief aid off Myanmar's coast to leave the area T after the ruling junta refused to give them permission to help survivors of last month's devastating cyclone.

Adm. Timothy Keating, the top commander in the Pacific, ordered the USS Essex and accompanying vessels to depart the Myanmar area after what he said were 15 separate attempts in recent weeks to get the junta's authorization to help with relief efforts.

Myanmar's state media has said it feared a U.S. invasion aimed at seizing the country's oil deposits.

The ruling generals also have forbidden the use of military helicopters from friendly neighboring nations, which are vital in rushing supplies to isolated survivors in the Irrawaddy delta. This has forced aid agencies to scour for civilian aircraft around the world and bring them in at dramatically increasing costs.

The U.N. has estimated 2.4 million people are in need of food, shelter or medical care as a result of the storm, which the government said killed 78,000 people and left another 56,000 missing.

Speaking in Hawaii on Tuesday, Keating said the U.S. unsuccessfully tried to persuade Myanmar's leaders to allow ships, helicopters and landing craft in to provide additional disaster relief.

The U.S. military ships were already in the region for international exercises when the cyclone hit. Keating made them available to help with relief efforts for the storm, and they were deployed near Myanmar in case they obtained permission to enter the country's waters.

But Myanmar allowed only limited U.S. military aid flights to the country, and barred the ships from approaching.

Paul Risley, a spokesman for the U.N. World Food Program, said the departure of the American ships meant relief agencies would not have the chance to take advantage of their fleet of helicopters.

"That is truly unfortunate because these helicopters represent immediate heavy-lift capacity in the area of the delta," Risley told reporters in Bangkok, Thailand.

Risley earlier warned that the logistical aspects of the relief operations, such as the chartering of helicopters, were causing expenses to soar.

In previous large scale disasters — such as the 2004 Indian Ocean tsunami and Pakistan's 2005 earthquake — military helicopters were used to meet the massive emergency's immediate requirements, he said. Thailand and Singapore have many helicopters on hand, he said.

"For political reasons, the Myanmar government was reluctant to approve their use," Risley said. Myanmar was reportedly able to field only seven helicopters of its own.

Amanda Pitt, a spokeswoman for the U.N. relief operation in Bangkok, said increased aid has reached survivors over the last few days, but access to the delta remains difficult.

"Much remains to be clarified as far as stepping up of the relief operation," she said. "We want better access for international aid workers ... both in terms of getting into the country and more consistent access to the delta areas."

The French aid agency Doctors Without Borders said its staffers were still finding remote areas in the delta which have not received any assistance from Myanmar or international sources.

Souheil Reaiche, the group's mission chief in Myanmar, also said that the affected population is higher than U.N. estimates because migrants and others not officially registered by authorities are found among survivors.

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 in a situation report dated June 2.

It said in Myanmar's Irrawaddy delta, the area hardest hit by Cyclone Nargis, the proportion of people reached with assistance had increased to 49 percent from 23 percent on May 25.

However, the report warned, "There remains a serious lack of sufficient and sustained humanitarian assistance for the affected populations."

Hiroyuki Konuma, an official of the U.N. Food and Agriculture Organization in Bangkok, expressed concern that if rice planting did not occur soon, farmers would "suffer from hunger and poverty for a long time while national food security will be seriously jeopardized."

He said that 60 percent of the paddy fields in the delta, the country's rice bowl, were hit hard by the cyclone but that only 16 percent are too damaged to be cultivated in the next planting season, which starts July.

But Konuma said few farmers were returning to their land because they lack food and shelter, basic agriculture tools and draft animals, while access to the land was difficult because so many road and bridges were destroyed.

Meanwhile, the U.N. Development Program announced it will provide 20,000 households in 250 delta villages with cash grants over the next six months to help survivors revive the farming, fisheries and poultry sectors.

"This will empower the survivors," said Hla Myint Hpu, who conducted the needs assessment for the project. "People want to keep their dignity. They want help to rebuild their livelihoods and get back on their feet."