Foreign aid groups pressed Myanmar on Tuesday to stop closing cyclone relief camps as international experts kicked off a mission to pin down the scale of the devastation a month after the storm.

Cyclone Nargis, the world's most deadly natural disaster since the 2004 Indian Ocean tsunami, is officially thought to have left 134,000 people dead or missing and 2.4 million destitute.

But many survivors have not yet been reached and Western nations and foreign aid groups complain the relief effort is being hampered by the inflexibility of Myanmar's military rulers.

"They've had a cyclone but they're not changing the rules. It's business as usual," said one official at an aid agency in Yangon, who asked not to be named.

Cumbersome regulations were blocking more vehicles and boats being used to distribute vital aid and even access to satellite communications was being made difficult, the official added.

Aid groups in Yangon held an emergency meeting on Tuesday to thrash out a common approach before a meeting with the Myanmar government in the afternoon, during which red tape and the closure of cyclone camps were due to be brought up.

Authorities have pushed ahead with a campaign, condemned by human rights groups and deemed "unacceptable" by the U.N., of evictions of displaced people from government shelters.

"If populations are on the move all the time, it's very hard to reach them," said Chris Webster, a spokesman for the charity World Vision in Yangon.

Closing the camps, usually clusters of tents around schools or other buildings, meant that growing numbers of displaced were returning to areas where the situation was already bad, said the first aid worker.

The last camp in Kawhmu, a district south of Yangon, was shut on Monday, witnesses said of the closures which appeared aimed at stopping the tented villages from becoming permanent.

SITUATION ON THE GROUND MURKY

The United Nations estimates that 1.3 million people had been given some assistance, although this was patchy and only half of those in the worst-hit delta had been reached.

"There remains a serious lack of sufficient and sustained humanitarian assistance for the affected populations," the U.N.'s humanitarian arm said in a report.

In the last week around 15 international staff had been allowed to travel to the delta, but agencies still had no permanent presence, it said.

World Food Programme boss Josette Sheeran said its $70 million (35 million pounds) food aid programme faced a 64 percent funding shortfall, as did its logistics plan which includes boats, trucks and helicopters.

"With current contributions, we will run out of food by mid-July," she said on Monday.

A United Nations "flash appeal" also remains well short of its $201 million target a month after the disaster.

The level of aid stands in stark contrast with the 2004 earthquake and tsunami in Indonesia's Aceh, when governments around the world promised $2 billion within the first week for a disaster which killed at least 232,000 people.

With the needs on the ground still so murky, an assessment team of experts led by Southeast Asian nations and the United Nations arrived in Yangon on Monday.

"Based on the assessment report that they will produce, we will be able to identify the needs of the Cyclone Nargis' victims and intensify our efforts in the most needed areas," said Surin Pitsuwan, secretary general of the Southeast Asian body ASEAN.

Southeast Asian nations have been seeking to take a leading role in relief efforts, particularly since Myanmar's generals have often been wary of accepting help from Western countries, whose patience also appears to have been wearing thin.