MOSCOW, Russia (AFP) — Moscow on Monday downplayed reports that a laboratory technician had died of plague, stressing that post-mortem tests had not detected the disease, while Washington said it was closely monitoring the situation.

Reports on Friday that plague had killed a 28-year-old woman named Darya Shipilova, who had been working for the anti-plague institute in Siberia’s Irkutsk region, sparked alarm.

The news outlet People of Baikal, citing unnamed sources close to the regional security services, said she may have contracted pneumonic plague from a broken test tube.

Other media reported a possible link between her death and a lab accident at the facility.

But Irkutsk regional governor Igor Kobzev said Monday that a special expert commission inspection in the region had found that “the cause of death was pneumonia of undetermined etiology”.

He said on Telegram that Russia’s consumer and health watchdog Rospotrebnadzor had determined, following tests, that “no microorganisms linked to the young woman’s professional work were found in her biological samples”.

He added that there had been “no new cases of staff from the anti-plague institute seeking medical attention” since the woman’s death.

Kobzev said the sanitary-epidemiological situation in Irkutsk was “stable”.

“The situation remains under our control and that of the experts.”

Asked about the situation on Monday, Kremlin spokesman Dmitry Peskov told reporters to “rely on Rospotrebnadzor’s official statements rather than … rumours and speculations”.

Plague is a bacterial disease that can occur in several forms, including pneumonic plague, the most contagious type. Pneumonic plague can be fatal if not treated early, according to the World Health Organization.

US Secretary of State Marco Rubio said his country was monitoring the situation but saw no “cause for alarm”.

“There’s very limited travel between the US and Russia, obviously, but like anything else, something like that gets out, it could quickly spread,” Rubio told reporters before taking off for a visit to Iceland.

“So we’re watching and monitoring it closely. I don’t think it’s cause for alarm, but it is cause for focus and a cause to just keep an eye on it. And we’re doing that.”