The UN has aired its "increasing frustration" at not being able to bring more help to the neediest survivors, and said the crisis in the country's remote, flooded south posed an "enormous logistic challenge".
Elisabeth Byrs, a spokeswoman for the UN's emergency relief arm, said it requires "at least an air or sea corridor to channel aid in large quantities as quickly as possible".
"We fear a second catastrophe," she said.
But the military government of Myanmar said on Tuesday that the needs of the people after the storm "have been fulfiled to an extent".
Vice-Admiral Soe Thein, a government spokesman, told the New Light of Myanmar newspaper: "The nation does not need skilled relief workers yet."
Aid trickles in
Only limited supplies have been allowed into the country so far.
An Australian air force plane landed in Yangon, Myanmar's main city, with 31 tonnes of emergency supplies, a day after the first US military aid flight arrived in the country.
Two more US flights arrived on Tuesday as part of a "confidence building" effort to prod Myanmar into allowing a larger international relief operation.
However, Al Jazeera's correspondents on the ground say government restrictions on aid agencies and the scale of the crisis means that the little aid getting into the country is not getting through to many badly-hit areas.
France, Britain and Germany on Tuesday urged nations to deliver aid to cyclone victims in Myanmar if necessary without the government's agreement.
Rama Yade, France's junior minister for human rights, said: "We have called for the 'responsibility to protect' to be applied in the case of Burma [Myanmar]."
The little-used UN principle could allow the delivery of aid without the accord of the government if Myanmar's military rulers continue to bar foreign aid teams from entering the country.
Aid agencies warn that as every day passes without sufficient food, water and shelter, more are at risk of joining the staggering death toll.
The World Health Organisation said it had dispatched supplies of body bags, as experts warned that corpses were going uncollected and that the putrefying remains pose a major health risk.
The UN also said that child traffickers are targeting the youngest and most vulnerable survivors of the catastrophe, and that two suspects have already been arrested after trying to recruit children at a relief camp.