Russia is keeping a tight lid on the death of a laboratory worker at a Siberian plague research institute, even as the World Health Organization presses Moscow for answers.

Darya Shipilova, 28, worked at the Irkutsk Anti-Plague Research Institute. She fell ill and died on October 2 of what officials called pneumonia of unknown origin. About 200 contacts were quarantined; officials say 60 per cent have since been released.

Russia told the WHO it has no registered plague cases in the Irkutsk region and that contacts tested negative for dangerous pathogens. But Moscow has shared few details, and state media have largely avoided the story.

The US has urged greater transparency, and Mongolia has stepped up health checks on its border with Russia. Kremlin spokesman Dmitry Peskov accused the media of spreading false reports.

Context: the WHO says it cannot complete a full risk assessment until Russia shares test details and contact health data.