Barack Obama said that not enough was being done to tackle the deadly Ebola outbreak in West Africa and called for more international aid.
"We are not moving fast enough. We are not doing enough," Obama told a meeting at the United Nations on the health crisis.
"Right now, everybody has the best of intentions, but people are not putting the kinds of resources necessary to put a stop to this epidemic," he said.
The meeting was called by UN Secretary General Ban Ki-moon to ramp up the international response to the world's worst Ebola epidemic, which has left close to 3,000 dead in Liberia, Sierra Leone and Guinea.
Health systems in the three countries have been overwhelmed and the United Nations has made repeated urgent appeals for more doctors, nurses, medical equipment and supplies to be sent to West Africa.
"The world can and must stop Ebola now," Ban said in his address to the meeting. "Today, it is time for the international community to step up."
Sierra Leone on Thursday took the drastic step of putting more than one million people in five districts under quarantine-- the largest open-ended lockdown in the Ebola outbreak.
The United States is sending 3,000 troops to Liberia to help health workers battle the contagion and has mobilized its experts from the Centers for Disease Control and Prevention to help beat back the virus.
The CDC estimates that cases in Liberia and Sierra Leone could rocket to 1.4 million by January -- in a worst-case scenario based on data obtained before the world ramped up its response.
Guinea President Alpha Conde was attending the meeting while Liberia's Ellen Johnson-Sirleaf and Ernest Bai Koroma of Sierra Leon were taking part by video-link from their countries.
Leaders from Japan, China, France, Germany were also due to take part.