YANGON, Myanmar—The official death toll nearly doubled to 78,000 from Myanmar’s killer cyclone as heavy rains on Friday lashed much of the area stricken two weeks ago, further hampering relief efforts.

Aid workers shackled by the country’s military regime struggled to get even the most basic data about the needs of up to 2.5 million survivors. The Red Cross warned that a lack of clean water may swell the ranks of the dead.

Myanmar state television said the official death count from the May 3 cyclone was 77,738, with 55,917 others missing.

The toll was nearly double the 43,000 previously reported, but the TV announcement suggested it might be close to a final figure. It said the government had “carried out search and rescue and relief work and collection of data, promptly, immediately and extensively.”

The release of the figures led to dire warnings from the United Nations and renewed calls for the military regime to allow international aid workers access to devastated areas.

“More than two weeks after the event, we are at a critical point,” said U.N. Secretary-General Ban Ki-moon. “Unless more aid gets into the country — quickly — we face the risk of an outbreak of infectious diseases that could dramatically worsen today’s crisis.”

Jean-Maurice Ripert, France’s ambassador to the U.N., criticized the junta for refusing to allow a French navy ship to deliver 1,500 tons of food, drugs and medication to the Irrawaddy delta using small boats.

He said refusing to allow aid to be delivered to those in need “could lead to a true crime against humanity if we go on like that.”

Myanmar’s ruling junta, meanwhile, put up a security cordon around Yangon to restrict travel to the Irrawaddy delta, where scenes of devastation were rife.

A small tour to the disaster zone arranged for Saturday will give diplomats their first up-close look at the effects of the cyclone and at the government relief effort.

John Holmes, U.N. undersecretary-general for humanitarian affairs, was to go to Myanmar on Sunday in an attempt to persuade the junta to admit more U.N. relief workers and to greatly increase aid efforts, said Amanda Pitt, a U.N. spokeswoman in Bangkok, Thailand.

“If you look at the situation with China, they have accepted relief and assistance teams from Russia, Taiwan and Japan,” Pitt said, referring to the response to the earthquake there. “They know they can’t do it on their own.”

The junta maintains it has the situation under control. But after two weeks, the U.N. remains largely in the dark about the situation on the ground.

“We simply don’t have the information, and I can’t say when we will have it,” said Steve Marshall, a U.N. official who just left Myanmar.

The Red Cross has put the death toll as high as 128,000 and the most recent official figures on dead and missing have the U.N. saying the number could easily reach 130,000.

The highest death estimate is carried by the British government’s Department for International Development, which says that “unofficial estimates suggest the number of dead or missing is in the region of 217,000.” The department said the estimate was reported to them by sources on the ground with knowledge of the situation.