UN-Myanmar
UN Secretary General Ban Ki-moon on Monday expressed his "immense frustration" at Myanmar government's slow response to the cyclone victims.
Ban said aid had been able to reach less than a third of all those at risk.
He said he had still not been able to speak to leader of Myanmar government, General Than Shwe.
Ban said that the reaction of Yangon government to the cyclone had been "unacceptably slow".
"We are at a critical point. Unless more aid gets into the country very quickly, we face an outbreak of infectious diseases that could dwarf today's current crisis," he said.
"I therefore call in the most strenuous terms on the government of Myanmar to put its people's lives first."
UN humanitarian head John Holmes said there had been "some slight improvement again in the last few days, particularly in the last 24 hours."
Thirty-four visas for UN staff were being granted or expected to be granted, he said.
But he added that this was "clearly nothing like enough for the scale of the problem we're trying to deal with".
In the Irrawaddy Delta, the area worst affected by the cyclone, people have been left without shelter, crops, and stored rice.
With little access to food or clean drinking water, they face cholera, fever and other illnesses.
Aid agencies have warned of serious logistical hurdles in getting supplies to affected areas.
Roads and bridges have been washed away, and heavy rain that fell on Monday is expected to further complicate relief efforts.
Ban said the UN had been able to reach some 270,000 people, providing only "the most rudimentary assistance".
He said that food aid provided so far might amount to less than a 10th of what was needed and that rice stocks were "close to exhaustion".