Irkutsk: Nearly 200 people are under medical observation in Siberia after the death of an employee at Russia's Irkutsk Anti Plague Research Institute, as authorities investigate reports of possible plague contraction.

Local media identified the employee as 28 year old laboratory technician. She became seriously ill with pneumonia and later died after being admitted to hospital.

The case produced conflicting accounts of the cause of her illness.

Alexei Tsydenov, head of the neighbouring Russian republic of Buryatia, said on October 3 that the woman "maybe" died of plague. Media reports also linked her illness to possible exposure at the research institute.

However, Russia's public health watchdog, Rospotrebnadzor, did not confirm that Shipilova contracted plague. It said she was diagnosed with pneumonia of unknown origin and that expanded testing found no microorganisms linked to her professional work.

The agency also said it recorded no accidents involving work with pathogenic microorganisms at the institute.

As a precaution, 189 people who were in contact with the woman were reportedly placed under medical observation. Irkutsk Governor Igor Kobzev said the identified contacts showed no signs of illness and that their laboratory tests were negative.

Russian authorities maintained that the epidemiological situation in Irkutsk and the nearby city of Shelekhov remains stable.

The case attracted international attention. A US State Department official said Washington was aware of reports of a suspected fatal case of pneumonic plague in Irkutsk and was monitoring developments in coordination with the US Centres for Disease Control and Prevention and other agencies.

Russian authorities did not officially identify plague as the cause of the laboratory worker's death, and no broader outbreak was confirmed.