He also denied claims that the disease had allegedly spread from the former Vozrozhdenia Island in the Aral Sea to the Uzbek-Kazakh frontline, where a Soviet biological weaponry testing range used to be.

"The site was mothballed long ago. It is under the control of appropriate ministries and agencies. No one lives on a radius of 200 kilometers around that site. As far as we know, there are no smallpox agents left there," he said.

The world has not had natural smallpox cases since 1978, the official said.