Image caption The viral disease was eradicated over 30 years ago

A decision on when to destroy the last known stocks of live smallpox virus has been put off for another three years.

The World Health Organization (WHO) agreed to resume the discussion in 2014, following debate this week at its annual meeting.

Countries were divided on the issue at the 64th World Health Assembly.

Iran led opposition to a plan backed by the US and Russia to set a date for destruction in 2016.

Smallpox facts Caused by the variola virus

The virus originated over 3,000 years ago in India or Egypt

Symptoms include fever, muscle pain, headache, tiredness and the distinctive rash

It killed 30% of those infected

More than 300 million people were thought to have died from smallpox in the 20th century alone

Up to 80% of survivors were marked with deep pitted scars, mostly on the face

There has been a lot of discussion around the smallpox issue," Pierre Formenty of the WHO told a news briefing in Geneva.

"Three years from now, we will resume the discussion."

The issue was first discussed at the Assembly in 1986 and has been the source of debate ever since.

Destroying the remaining stocks of variola, or small pox virus, is seen by some countries as the final chapter in eradicating the disease to prevent the risk of accidental release.

Others, including the US and Russia, argue for more research in case smallpox returns, possibly as a biological weapon.