THE Myanmar military junta's delay in allowing international aid into the cyclone-hit country cost 'tens of thousands of lives', United States Defence Secretary Robert Gates said.

Speaking at a top-level security conference here on Saturday, Mr Gates said US ships could have quickly delivered much needed aid to Myanmar in the aftermath of the May 2-3 storm that left 133,000 people dead or missing.

'Our ships and aircraft awaited country approval so they could act promptly to save thousands of lives - approval of the kind granted by Indonesia immediately after the 2004 tsunami and by Bangladesh after a fierce cyclone just last November,' Mr Gates told the regional forum.

'With Burma, the situation has been very different - at a cost of tens of thousands of lives.' Mr Gates added that many other countries besides the United States have also felt hindered in their efforts to help Myanmar recover from Cyclone Nargis.

'My own view is that that (force) will be a serious mistake and it clearly has been a policy of our government and we don't expect it to change.' Nearly four weeks after the cyclone pummelled large swathes of Myanmar, foreign aid has still only reached 40 per cent of the 2.4 million needy survivors, the United Nations said.

Inciting international outrage, Myanmar's isolated military had largely barred foreign aid workers from gaining access to the south-west Irrawaddy Delta, which bore the brunt of the cyclone.

Relief workers slowly moved into the delta on Thursday after the junta started to ease restrictions on access.

The United Nations said on Friday it has received all the visas it had requested from Myanmar for its disaster aid workers but called for unhindered access for other humanitarian workers and groups.

US war ships carrying relief supplies have been off the coast of Myanmar for two weeks waiting for Myanmar's permission to move in. US military planes, however, have been allowed to land in the main city Yangon to deliver aid.

Mr Gates also told the seventh Shangri-La Dialogue that the US welcomed Asean's leadership, and looked forward to the quick emergence of a mechanism that can help international assistance reach those who need it.

Singapore holds the current chair of the 10-member Association of South-east Asian Nations (Asean), of which Myanmar is a member.

An assessment team from Asean was set to arrive in Yangon on Friday to determine how best to help the survivors in desperate need of food, shelter and medicine.

In a keynote opening address to the Shangri-La Dialogue on Friday night, Singapore's prime minister said Myanmar's response to foreign offers of help for cyclone victims is regrettable.

'It's regrettable that the Myanmar government has responded in this way. Myanmar's partners in Asean have all been deeply concerned by the massive suffering of the victims, which a more rapid international relief operation could have minimised,' Prime Minister Lee Hsien Loong said.

Criticism also came from White House spokesman Dana Perino in Washington on Friday. She said the Myanmar junta's response to the crisis 'continues to frustrate not just the United States, but other countries, and certainly the non-governmental organisations that are trying to get in there'.

In an apparent reference to the United States, the New Light of Myanmar newspaper, a government mouthpiece, on Friday criticised countries for maintaining sanctions on the regime despite the cyclone devastation.

The US renewed sanctions two weeks after the storm, accusing Myanmar's junta of suppressing the pro-democracy movement, while insisting the sanctions will not affect humanitarian aid.

Also known as the Asia Security Summit, the Singapore meeting of defence and national security officials and analysts is organised by the London-based International Institute for Strategic Studies, an independent think-tank. -- AFP