The World Health Organization (WHO) on Friday delayed for at least four years any decision on when to destroy the world's last known stockpiles of smallpox, a deadly virus eradicated nearly 30 years ago.

There is no treatment for the virus that was killing millions of people a year as recently as the 1960s and left many more blind and scarred. In 1979, it became the first disease officially stamped out after a worldwide vaccination campaign.

But the United States and Russia, which hold the only known stockpiles of the virus in high-security laboratories, have long resisted calls to destroy them in case smallpox is found to exist elsewhere.

The 60th annual World Health Assembly, the top decision-taking body of the United Nations agency, reaffirmed a previous commitment to getting rid of the remaining stockpiles but agreed to postpone any decision on when this should happen until its 2011 meeting.

In 2010, the WHO secretariat will carry out a review of all research undertaken and still planned in order that the "64th World Health Assembly may reach global consensus on the timing of the destruction of existing variola virus stocks."

A previous 2002 deadline for destroying smallpox had been waived by the WHO until new vaccines or treatments for smallpox were found, after the United States said it would keep stocks on hand to combat any re-emergence of the disease.

That decision was taken in the wake of the September 11 suicide plane attacks on the United States which stirred fears that deadly viruses could fall into the hands of terrorist groups.