U.N. Secretary-General Ban Ki-moon toured Burma's cyclone-ravaged Irrawaddy Delta Thursday as he pressed the country's leaders to accept more international aid for 2.5 million survivors.

Mr. Ban's helicopter tour flew over some of the worst-hit areas and stopped at relief camps. The U.N. chief urged one woman not to lose hope and said, "the United Nations is here to help you."

Before his three-hour inspection tour, Mr. Ban met with the Burmese Prime Minister, General Thein Sein, in the main city of Rangoon. Mr. Ban said the gravity of the disaster is beyond Burma's capability and that the country requires international assistance. General Thein Sein said the relief phase was over and that it is now time to begin reconstruction.

The secretary-general of the Association of South East Asian Nations (ASEAN), Surin Pitsuwan, criticized the general's remark, saying the full extent of the disaster has yet to be verified.

The U.N. chief is expected to meet Burma's leading general, Than Shwe, Friday in the capital, Naypyidaw. Mr. Ban has been unable to get the general to take his phone calls or respond to his letters in the aftermath of the cyclone.

Mr. Ban is scheduled to fly back to Bangkok on Friday, and then return to Burma on Sunday for a donors' conference organized by the United Nations and the Association of Southeast Asian Nations.

The U.N. says help has only reached 25 percent of the people affected by Cyclone Nargis. Humanitarian agencies warn that more people could die from lack of food, water and shelter. Mr. Ban has repeatedly warned that the crisis could continue if farmers are unable to plant the next crops.

Several U.S. military cargo planes carrying aid were allowed to land Thursday. But Burmese authorities have refused to permit U.S. Navy ships stationed off the coast of Burma to deliver tons of relief for cyclone victims.

Burma allowed U.S. relief expert William Berger to join a government-led tour of the disaster zone on Thursday and Friday aimed at assessing how much aid is needed. Berger is the first U.S. government relief official to be allowed into the country since the cyclone ravaged Burma's Irrawaddy Delta on May 3. The U.S. State Department said on Thursday that Berger's colleagues remain in Bangkok because they were not granted visas.

Burmese military leaders say the cyclone that hit May 3 killed an estimated 78,000 people, and that 56,000 others are still missing. They have asked for $11 billion in foreign assistance.

Some information for this report was provided by AFP, AP and Reuters.