Foreign aid agencies urged Burma's, also known as Myanmar, junta Saturday to urgently clarify rules for operating in the country's cyclone-devastated areas, expressing hope tinged with cynicism after the regime promised to open its doors to the international community.

Burma's ruling generals offered no elaboration after U.N. Secretary-General Ban Ki-moon's announced Friday that the junta had agreed to allow "all aid workers" into the country.

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The concession came after three weeks of blocking relief for cyclone survivors, and on the eve of an international donors' conference Sunday in Burma.

"I want to be optimistic, but I'm skeptical," Lionel Rosenblatt, president emeritus of U.S.-based Refugees International said, voicing comments echoed by relief agencies worldwide. "My overall impression is skepticism and what this actually means. The devil is going to be in the implementation."

The possible breakthrough distracted attention from the junta's widely criticized decision to push ahead Saturday with a constitutional referendum in Rangoon, Burma's largest city, and hard-hit areas of the Irrawaddy River delta.

Critics have said that the proposed charter is designed to strengthen the military's grip on power, and that they had urged the government to focus on relief efforts.

Many viewed Saturday's voting as a pointless exercise. The rest of the country voted May 10, and state radio has said the delayed balloting could not reverse the constitution's reported approval by 92.4 percent of the 22 million eligible voters.

Detained democracy leader Aung San Suu Kyi cast her ballot on Friday evening when referendum officials visited her Rangoon home with a ballot card, an official said on condition of anonymity. Suu Kyi's opposition party called for a "No" vote on the proposed charter, which effectively bars her from holding elected office.

Suu Kyi's home was damaged during the May 2-3 cyclone, which decimated the Irrawaddy delta, Burma's key rice-producing region in the southwest.

The xenophobic junta has kept the delta virtually off-limits to foreign aid workers, who have been barred from traveling outside Rangoon.

The push to get aid workers into the delta is increasingly urgent because an estimated 2.5 million people remain in severe need, threatened by disease, hunger and exposure due to the loss of their homes.

"It is a race against time to get aid to the people who desperately need it," the British aid group Oxfam said in a statement, adding it "cautiously welcomed" the junta's new willingness to accept foreign experts but was waiting to see "genuine efforts to relieve the suffering on the ground."

Aid agencies said that much needs to be clarified from Ban's meeting, ranging from logistical issues about when aid workers' visas will be granted to how long they will be allowed to stay in Burma and where they can work.

"We're hopeful that it means more foreign aid workers will go to the worst-affected areas," said Save the Children spokeswoman Kate Conradt. "We already have a number of expatriate staff in Yangon. They just can't leave the city."

The U.S.-based International Rescue Committee said in a statement it is "still seeking clarity" and hoped aid workers will truly have "unhindered access to deliver aid."

Official estimates put the death toll at about 78,000, with another 56,000 missing. Burma has estimated the economic damage at about $11 billion.

Under intense international pressure — and with an aid donors' meeting scheduled for Sunday — Senior Gen. Than Shwe said he would allow aid workers into the affected area "regardless of nationality," Ban said Friday.

Than Shwe refused to relent on the landing of military ships, however.

According to Ban, Than Shwe "agreed that international aid could be delivered to Burma via civilian ships and small boats."

The U.S., Britain and France all have warships off Burma's coast ready to help, but they have not been given approval to go ashore or send helicopters to bring aid to the most remote and desperate areas. Burma's junta is nervous about any shore landings because it fears an invasion or political interference.

Ban flew to Chengdu in China on Saturday to inspect the damage from the May 12 earthquake there. While touring earthquake-hit areas, Chinese Premier Wen Jiabao said China will pledge $10 million in aid for Burma at Sunday's conference.

Ban was scheduled to fly to Bangkok later Saturday to join Thai Prime Minister Samak Sundaravej in opening a staging center for cyclone relief supplies at the city's Don Muang airport.

The U.N. chief was expected to return to Rangoon on Sunday to co-chair the donors conference, which would be attended by officials from more than 45 countries and regional organizations, U.N. deputy spokeswoman Marie Okabe said Friday in New York.

The conference is being sponsored by the U.N. and the 10-country Association of Southeast Asian Nations, which is taking the lead in organizing the delivery of aid to Burma, one of its members.

ASEAN Secretary-General Surin Pitsuwan said he believed donors would be unlikely to honor pledges if the junta failed to follow through on its promises for international access.

"If the agreement given to the secretary-general of the United Nations cannot be implemented in spirit, then we will have problems delivering assistance," he said by telephone.

The United Nations has launched an emergency appeal for $201 million. That figure will likely increase further once disaster relief experts are able to survey the Irrawaddy delta.

So far the U.N. has received about $50 million in contributions and about $42.5 million in pledges in response to the appeal, said Stephanie Bunker, spokeswoman for the U.N. Office for the Coordination of Humanitarian Affairs.

Ban said Friday that the details of moving aid workers into the delta still needed to be worked out. But he stressed he believed he had achieved a breakthrough.

"I believe they will keep and honor their commitment," Ban said.

The junta allowed Ban to fly to the remote capital of Naypyitaw early Friday after taking him on a carefully choreographed, four-hour helicopter tour of the disaster zone on Thursday.

"I am humbled — humbled by the scale of this natural disaster," he said afterward.