Six U.S. military planes arrived in the Ebola hot zone Thursday with more Marines, as West Africa's leaders pleaded for the world's help in dealing with a crisis that one called "a tragedy unforeseen in modern times."

"Our people are dying," Sierra Leone President Ernest Bai Koroma lamented by videoconference at a World Bank meeting in Washington. He said other countries are not responding fast enough while children are orphaned and infected doctors and nurses are lost to the disease.

Alpha Conde of Guinea said the region's countries are in "a very fragile situation."

Ebola is "an international threat and deserves an international response," he said, speaking through a translator as he sought money, medicine, equipment and training for health care workers.

Tom Frieden, director of the U.S. Centers for Disease Control and Prevention, said he was reminded of the start of the AIDS epidemic.

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