"This is a big boost in the U.N. cyclone response capacity," said Risley. "The helicopters will multiply the work of the first helicopter, which has been shuttling food and humanitarian assistance."
He said a final four helicopters for WFP use, now in Bangkok, are expected to fly to Myanmar in the coming week.
The relief effort, however, still faces a myriad of problems, among them a severe shortage of housing materials that could leave hundreds of thousands of survivors exposed to heavy rains as the monsoon season begins, aid agencies said.
The United Nations and the International Federation of Red Cross and Red Crescent Societies warned there was an "urgent need" for tarpaulins to provide the estimated 1.5 million homeless survivors with temporary shelter. Otherwise, they warned, the threats of hunger and disease could intensify.
"Exposure to the elements five weeks after a disaster of this magnitude has to be a major concern," said John Sparrow, a spokesman for the IFRC. "People are in a weakened condition. They are sick; they are hungry. Without shelter, their whole situation is seriously exacerbated."
Tarpaulin supplies within Myanmar have run out, and the market for items such as shelter materials is very tight because of the demand from China's earthquake victims as well, the U.N. said.
Its ad hoc group to coordinate emergency shelter for Myanmar warned that the "potential for price gouging is high."
The U.N.'s Office for the Coordination of Humanitarian Affairs warned that funding for its logistics operation has to be stepped up. Only $20 million of the $50 million required has been received.
"These funds are needed to extend the outreach of the operation from the hubs to those villages that have yet to receive assistance," said OCHA in its latest situation report.
OCHA also indicated that foreign relief workers still face hindrances in reaching cyclone victims, especially outside of Yangon.
While U.N. staff face no reported obstacles in obtaining visas to Myanmar, the visa process for international humanitarian groups "still seems to be more cumbersome," and some of them have visa requests that have been pending for up to three weeks.
It added that the process to obtain authorization to travel to the Irrawaddy delta is taking more than two to three days.
The U.N. estimates a total of 2.4 million people were affected by Cyclone Nargis, and warns that more than 1 million of those still need help, mostly in the hard-to-reach Irrawaddy delta.
U.N. officials and aid groups have criticized the regime for restricting access to the delta, saying it has prevented enough food, water and shelter from reaching desperate survivors.
The top U.N. humanitarian official said Friday in New York there are now "relatively few people" who have not received any sort of help, but "this aid effort needs to be stepped up further," he said.
"I think people are getting to all the main places, although it's not always as easy as it should be," John Holmes said. "There's no evidence of starvation at the moment, although, as I say, many people are still in significant need of aid."
With only seven Myanmar government helicopters reportedly flying, relief supplies are mostly being transported along dirt roads and then by boat. International aid agencies say boats able to navigate the delta's canals are scarce and efforts to import vehicles have been hampered by government red tape.
The junta has rejected repeated offers by the U.S. military to allow its helicopters to transport assistance to the delta.
Myanmar's junta, long shunned by Western governments because of its poor human rights record and failure to hand over power to a democratically elected government, remains sensitive to foreign criticism.
Reports in the state-owned New Light of Myanmar newspaper on Friday lashed out at the country's own citizens and foreign media for what it called distorted coverage of the cyclone's aftermath.
On Saturday, the newspaper dismissed as "groundless" allegations that survivors are being dumped near their devastated villages in the delta without any assistance.
"It is a storm of rumors designed to deal a devastating blow to our country," said a commentary in the newspaper.
It said such rumors were "invented and circulated by certain Western countries" and their puppets inside and outside the country.
"In other words, it is just a scheme conspired by a crafty tiger that is desperate to eat the flesh and the fox that is waiting for leftovers."