The World Health Organisation on Monday held a stormy discussion on the future of smallpox virus samples, which Russia and the United States are seeking to preserve while others want them destroyed.
The question surrounding the destruction of the last official stocks of the deadly virus held by US and Russian laboratories has been recurring at the WHO since 1986.
Washington and Moscow want the viruses kept for scientific reasons, saying that it is necessary to continue research on their vaccines in order to prevent any resurgence of the transmissible disease which was eradicated in 1979.
They fear in particular that countries may have secretly kept the virus to be used as a biological weapon.
In a draft resolution put forward Monday to the 193 WHO member states, Russia and the US once again sought to conserve the samples, and wanted to begin discussing a possible date for their destruction only in five years.
Many countries want them destroyed immediately however and, amid the discord, the WHO decided to create a working group to work towards a compromise draft.
The debate will continue on Tuesday, a WHO spokeswoman said, ahead of a eventual vote on the resolution.
"Nothing is to be expected tonight on smallpox," said Fadela Chaib.
"The informal working group resumed its work at 17:30 pm (1530GMT). They will work for a couple of hours in a private session.
"They will then report back to the Committee A tomorrow morning."
The Russian envoy said during Monday's discussion: "We feel that we do not have sufficient guarantees on the efficiency and the preparation of the vaccines."
"Destruction will be irreversible," he added, noting that it is necessary to be "doubly prudent on a question that concerns security of all humanity."
"After the research, we can determine a date," he added.
The European Union, Canada, Israel, Monaco, Colombia and China were among countries that supported the move.
However, some 20 countries, including north African states, Iran, Thailand, Zimbabwe and Malaysia, were strongly against the resolution, saying that immediate destruction of the virus must be imposed.
"There is no longer scientific justification to keep these viruses," said a Malaysian diplomat.
"It's been 30 years since we agreed to keep the stocks," noted an Iranian envoy. "It is about time to fix a definitive date" to eradicate them.
Aid groups also spoke out against retaining the virus.
Edward Hammond, an adviser to Third World Network, said smallpox was "a question of national security for the US and Russia, hidden behind a health mask."