US President Barack Obama had said stopping the current outbreak of the Ebola virus in west Africa was a priority for the United States.
If not stopped, he said, the outbreak "could cause a humanitarian catastrophe across the region".
Speaking at a meeting on the sidelines of the UN General Assembly, Mr Obama said that there was still a "significant gap between where we are and where we need to be" in the international response to the outbreak.
"More nations need to contribute critical assets and capabilities - whether it's air transport, medical evacuation, health care workers, equipment, or treatment," he said.
UN Secretary General Ban Ki-moon said today that the world could and must stop Ebola now.
The worst outbreak on record of the deadly virus has left close to 3,000 people dead in west Africa.
This evening, the world's most developed economies pledged to keep open air and sea links with Ebola-hit countries.
They said much-needed help had to be able to reach those nations battling the epidemic.
"We warn that although the spread of Ebola must be contained, affected countries must not be isolated," the G7 group said, calling for medical help and equipment in fighting the outbreak.
The G7 said it would also coordinate to ensure the care and evacuation of any foreign health workers who are infected by the disease.
Meanwhile, doctors in the US have said that a third US Ebola patient, who was being treated in Nebraska, was now free from the virus.
The spread of Ebola seems to have stabilised in Guinea, one of three west African states worst hit by the disease.
However, a lack of beds and resistance in affected communities means its advance continues elsewhere, the World Health Organisation said today.
In a bid to halt the outbreak, Sierra Leone put three more districts - home to more than a million people and major mining operations - under indefinite quarantine.
An outbreak that began in a remote corner of Guinea has taken hold of much of neighbouring Liberia and Sierra Leone, killing nearly 3,000 people in just over six months.
World leaders and international organisations have warned of a crisis threatening the stability and economies of a string of fragile west African states. But they have also been criticised for doing too little too late.
"The upward epidemic trend continues in Sierra Leone and most probably also in Liberia," the WHO said in its latest update on the disease, which has killed about half of those confirmed and suspected to have been infected.
WHO said earlier this week that the total number of infections could reach 20,000 by November, months earlier than previously forecast.
The US Centers for Disease Control and Prevention (CDC) warned between 550,000 and 1.4m people might be infected in the region by January if nothing was done.
