A virus frozen in Siberia for around 30,000 years has been brought back to life after being uncovered by scientists.
The discovery of the virus, named Pithovirus sibericum, under 30m (100ft) of frost has prompted fears that other hidden strains such as smallpox could be exposed by the effects of global warming.
France's National Centre for Scientific Research, which was responsible for the finding in the Chukotka autonomous region, said in a release on its website that the findings "have important implications in terms of public health risks".
"The re-emergence of viruses considered to be eradicated, such as smallpox, whose replication process is similar to Pithovirus, is no longer the domain of science fiction," the organisation said. "The probability of this type of scenario needs to be estimated realistically."