The top government spokesman said that Tokyo stands ready to offer an experimental drug developed by a Japanese company to help stem the global tide of the deadly Ebola virus.
"Our country is prepared to provide the yet-to-be approved drug in cooperation with the manufacturer if the WHO requests," Chief Cabinet Secretary Yoshihide Suga.
The World Health Organization (WHO) has been discussing the use of unapproved drugs as a way of getting a handle on an outbreak in Africa that has already cost more than 1,400 lives, with thousands more people infected.
There is currently no available cure or vaccine for Ebola, and the WHO has declared the latest outbreak a global public health emergency.
Several drugs are under development.
The use of an experimental drug called ZMapp on two Americans and a Spanish priest infected with the virus while working in Africa has opened up an intense ethical debate.
The drug, which is in very short supply, has reportedly shown promising results in the two Americans, although the priest died.
US company Mapp Bioparmaceutical which makes the drug said this month it had sent all its available supplies to west Africa.
The WHO earlier said a panel of medical experts had determined it is "ethical" to provide experimental treatments.
Suga said Monday: "Even before the WHO reaches a conclusion, we are ready to respond to individual requests (from medical workers) under certain conditions if it is an urgent case."
The medication Suga was referring to is Avigan, a drug in tablet form that was approved as an anti-influenza drug in Japan in March and is currently in clinical tests in the United States.
Its developer Fujifilm Holdings said it had received inquiries from abroad but declined to say how many and from which countries.
The company, which has diversified into healthcare fields, has "no problem" over the amount of stockpiles, according to spokesman Takao Aoki.
"We have sufficient supplies for more than 20,000 people," he said.