Nearly 200 people have been placed under medical observation in Russia's Irkutsk region in eastern Siberia over suspected exposure to plague, according to local media reports.

The report said 189 people were being monitored following the illness of an employee at an anti-plague research institute in Irkutsk. Alexei Tsydenov, head of the nearby Republic of Buryatia, said the woman had died from an unspecified form of plague.

Russia's public health watchdog Rospotrebnadzor said Sunday that the employee had been diagnosed with "pneumonia of unknown etiology" and that the sanitary and epidemiological situation in the Irkutsk region and the cities of Irkutsk and Shelekhov remained stable.

The agency said expanded testing had not detected microorganisms linked to the employee's work.

The update follows local media reports on Friday that a 27-year-old employee at an anti-plague institute had fallen ill with suspected pneumonic plague after returning from a work trip to Buryatia, where an outbreak had been reported near the border with Mongolia, citing Russian Telegram channel Mash.

The White House is monitoring reports of the suspected case and related quarantines in Russia, Axios reported Sunday, citing a Trump administration official. The official said the administration was "aware, monitoring the outbreak, and assessing options," the report said.

The Russian and Moscow ministries of health, the World Health Organization and the U.S. State Department did not immediately respond to CNBC's requests for comment.