Yangon  - Flags were flying at half-mast at all government buildings Tuesday as Myanmar officially launched three days of belated mourning for some 133,000 victims of Cyclone Nargis which smashed in to the country's central coast 18 days ago.

State media announced three days of mourning for the catastrophe's victims Monday night, without providing an explanation as to why the government had taken so long to publicly grieve for the estimated 133,650 left dead or missing by the cyclone, which swept over Myanmar's central coast on May 2 to 3.

The public show of grief has coincided with the visit of United Nations Secretary General Ban Ki-moon, who is scheduled to arrive on Wednesday evening, and UN humanitarian affairs chief John Holmes, who arrived in Myanmar Sunday and visited three towns in the storm-devastated Irrawaddy delta on Monday.

Although Holmes was not granted an audience with government officials on Monday, a Buddhist holiday in Myanmar, we was to meet with senior officials including, possibly, Prime Minister Thein Sein on Tuesday.

"He's meeting some government officials and possibly the prime minister as well," said Aye Win, spokesman for the United Nations Information Centre in Yangon.

There are hopes that these high-level UN visits will put pressure on Myanmar's ruling junta to ramp up the international disaster relief effort for their own people, some 2.4 million of whom have been affected by the storm, according to UN estimates.

More than two weeks after Cyclone Nargis, the World Food Programme (WFP) has only been able to reach about one third of the 750,000 people deemed in desperate need of food aid.

The international aid community wants to see Myanmar's military regime ease restrictions on the massive logistical pipeline needed to get emergency supplies to the remote areas in the Irrawaddy delta where most of the cyclone's victims are.

The junta is also under pressure to grant more visas to foreign relief experts, and to allow more international aid workers into the Irrawaddy delta, which is currently off-limits for the vast majority of foreign aid workers.

Ban, who has been unusually outspoken over the last week about Myanmar's refusal to allow outside help in, was scheduled to leave New York Tuesday and arrive in Yangon on Wednesday for a meeting with Myanmar's senior government officials, spokeswoman Michelle Montas said.

"The secretary general was invited to come," Montas said, adding that the invitation was forwarded to Ban by Myanmar's UN ambassador.

Following the talks in Yangon, Ban will be in Bangkok for discussions with Thai officials on the Myanmar situation and then return to Yangon on Sunday for the UN-ASEAN conference, which was designed to scale up relief activities that have been so far restricted by the military junta in Myanmar.

The UN and the Association of South-East Asian Nations (ASEAN) have urged governments to send ministers to the meeting in Yangon, hoping that their presence would increase pressure on Myanmar to open its doors to international relief aid and workers.

"The conference will focus on the needs of those affected by the cyclone, and seek international support and financial assistance for the international humanitarian response to meet the most urgent challenges, as well as longer term recovery efforts," the UN said.

Both the UN and ASEAN urged the international community "to rise to the occasion and translate their solidarity and sympathy into concrete commitments to help the people of Myanmar emerge from the tragedy and rebuild their lives." (dpa)