The United States has warned Burma's military rulers they must cooperate with United Nations mediator Ibrahim Gambari or face increased pressure from the Security Council.

US ambassador Zalmay Khalilzad says the council expects "concrete results" from the UN troubleshooter's visit to Burma next month.

Meanwhile, the UN humanitarian envoy, John Holmes, says aid money for Burma in the wake of Cyclone Nargis is getting to those in need.

Total spending on relief is expected to reach $US500 million, while the rebuilding effort will tally about a billion dollars.

Mr Holmes, who has just returned from a visit to the isolated nation, says independent monitoring is being done through agencies working on the ground and the diplomatic missions inside the isolated nation.

I think there is a reasonable assurance that money is getting through to the people who really need it," he said.

Mr Holmes spent three days visiting the Irrawaddy Delta, hardest hit when cyclone Nargis struck on May 2.

He says he saw great improvements since his last visit almost two months ago, but people in the remotest areas are still in need of basic supplies.

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