In addition, the country's military government still hadn't issued visas to U.N. teams seeking to deliver the aid to parts of the country impacted by Cyclone Nargis, amid fears that lack of food and fresh water and waterborne illnesses could raise the death toll to more than 100,000.
Myanmar's generals issued an appeal for international assistance after the cyclone struck, but have since been slow in processing visas for relief workers.
Two airplanes containing high-energy biscuits, medicine and supplies arrived in Yangon, and two more were to follow, U.N. officials said, according to the Associated Press. The planes waited the last two days while U.N. and Myanmar officials negotiated their entry.
"What is critically needed at this point is for Myanmar authorities to open up to a major international relief effort," said U.N. spokesman Richard Horesy. "If that is not done quickly, there is a major risk that there will be a second phase to this disaster where large numbers of people will die of communicable disease."
The U.S. military sent more humanitarian supplies and equipment aboard airplanes to a staging area in Thailand.
Thai Prime Minister Samak Sundaravej offered to negotiate on behalf of the United States to persuade the military junta to permit the supplies, the AP reported.
The U.S. government and private donors also have committed over $1.5 billion in aid.
The Association of Southeast Nations, or ASEAN, appealed to other countries to keep sending aid through Thailand.
"Please keep the help coming, keep the contributions coming, and if you have to, go to Thailand, park there and wait for redistribution from there," said ASEAN Secretary-General Surin Pitsuwan, quoted the AP.
Myanmar's main ally, China, which pledged $5.3 million in aid, also urged the military regime to work with the international community.
Myanmar state media said the cyclone killed 22,997 people with 42,019 still missing. Shari Villarosa, who heads the U.S. Embassy in Yangon, said Wednesday that the toll could eventually surpass 100,000 as conditions in the country worsen.
Entire villages were flattened by the cyclone, especially in the low-lying Irrawaddy delta region.