Aid shipments for Burma are loaded in neighbouring Thailand. The Burmese regime is slowly relaxing tight restrictions on aid work, with more than a million survivors still in acute need of food, water, medicine and shelter. (David Longstreath/Associated Press)

Hundreds of foreign humanitarian relief experts began assessing the needs of Burma's millions of cyclone victims Tuesday as the country's military junta finally gave them access to storm-hit areas five weeks after the disaster.

Some 250 aid workers from United Nations agencies along with Burmese civil servants and officials from Southeast Asian countries headed into the Irrawaddy Delta by truck, boat and helicopter for a village-by-village survey, the UN said.

Over the next 10 days, they will determine how much food, clean water and temporary shelter the 2.4 million survivors need, along with the cost of rebuilding houses and schools and reviving the rice-based economy.

"It has taken quite a long time, but this shows the government is on board by its commitment to facilitate the relief operation and the scaling up that people are asking for," said Amanda Pitt, a UN spokeswoman in Bangkok.

Aid agencies estimate more than one million storm survivors, mostly in the delta, still need acute help. Cyclone Nargis killed more than 78,000 people in impoverished Burma, also known as Myanmar. More than 58,000 are still missing and unaccounted for.

The information collected will be released in a report next month by the Association of Southeast Asian Nations and should motivate more countries to donate to the cyclone relief operation, Pitt said.

Helicopters delivering assistance

The assessment began a day after UN-chartered helicopters began ferrying food and emergency supplies to Irrawaddy Delta communities still cut off by washed-out roads and floods.

The reclusive military junta in Burma has been sharply criticized by foreign governments and aid agencies for its inept handling of the disaster. It also has come under fire for forcing survivors from camps and allegedly dumping them in their destroyed villages.

Repressive actions by the government continued Tuesday, even as the foreign aid experts went to the Irrawaddy Delta to begin their assessment mission.

In Rangoon, authorities detained 18 women and children as they walked to UN offices to complain about not receiving assistance, according to a government official who refused to be identified for fear of retaliation by the leadership.

The marchers were bundled into a waiting police car and remained in detention, witnesses said.

The UN's Pitt said she was unaware of the arrests.

Suu Kyi supporters released

The criticism of the junta's aid effort comes on top of long-standing concerns about its poor record on human rights, including its detention of Nobel Peace Prize laureate and pro-democracy leader Aung San Suu Kyi.

On Tuesday, the junta released 15 members of Suu Kyi's party who were detained last month for demanding her release, a party spokesman said.

Suu Kyi has been held under house arrest for more than 12 of the past 18 years. Last month, the government extended her detention by another year.

The notoriously xenophobic Burmese military regime has been resisting many outside efforts to help cyclone survivors, shunning assistance from the U.S., French and British navies because of fears of being invaded, state media said.

With files from the Associated Press