Russia's consumer watchdog, Rospotrebnadzor, has confirmed that an employee at an Irkutsk anti-plague institute has an illness of "undetermined cause", Kommersant reported on October 4.

According to reports from Russia, Darya Shipilova, 28, is believed to be the person who died following an as-yet-alleged "lab accident", according to some sources, at the Irkutsk Anti-Plague Institute in Siberia.

The Russian health authority Rospotrebnadzor had earlier denied that the employee died of plague, and nearly 200 people were placed under medical observation after the reported death, IntelliNews previously reported.

Russian-language Kursiv reported earlier that the watchdog described pneumonia of undetermined origin, while the new statement describes an infection of "undetermined aetiology".

The watchdog said the epidemiological situation in Irkutsk region remains stable after media reports of a possible plague case. It said plague has not been officially confirmed and that it is continuing to assess the situation in the region.

Separate reports suggest that several hospitals in the region are now on lockdown.  Media reports of a possible plague case appeared before the statement and have spread online in recent hours.

Irkutsk Governor Igor Kobzev convened an emergency meeting of the regional sanitary and epidemiological commission with Russia's chief state sanitary doctor Anna Popova, and Rospotrebnadzor approved an operational action plan.

Local authorities asked residents to limit visits to Shelekhov and neighbouring towns, and a city clean-up planned in Irkutsk on October 3 was postponed for safety reasons.

The Irkutsk Aluminium Plant, which has 2,154 employees, introduced mandatory masks. Plant director Artyom Fominykh announced the move on Telegram.

"We have introduced a mask protocol at the facility as a precaution. God protects the cautious, so follow safety measures. If symptoms appear, seek medical help immediately," Fominykh said, Stolitsa na Onego reported. He added that Rospotrebnadzor was carrying out the necessary procedures and that identified contacts showed no signs of illness.

Gennady Onishchenko, an epidemiologist and academician of the Russian Academy of Sciences, said the infection was "likely not plague", while noting that specialists have treatment and prevention protocols if it is confirmed.

Uzbekistan strengthened sanitary controls at its borders after the incident with no plague cases have been confirmed in the country.