Dozens of people were reportedly placed in isolation after a laboratory worker at a Russian institute studying plague and other infectious diseases died from an undisclosed illness. The case has prompted quarantine measures, official scrutiny and concern in neighboring countries.

The researcher was a 28 year old female laboratory technician at the Irkutsk Research Anti-Plague Institute of Siberia in Shelekhov. She died after being diagnosed with pneumonia of “unknown” origin, according to Rospotrebnadzor, Russia’s infectious disease agency.

Local media identified the researcher as Darya Shipilova. Rospotrebnadzor sought to play down any connection between her death and her professional work at the institute.

“No micro-organisms associated with the employee’s professional duties were detected in samples taken from the patient,” the agency said. It also maintained that the region’s epidemiological situation was stable.

Despite those assurances, Rospotrebnadzor head Anna Popova traveled to Irkutsk on Friday. Regional governor Igor Kobzev said she attended an extraordinary meeting of a commission addressing epidemics.

Kobzev said on Telegram that the meeting concerned a “suspected case of a particularly dangerous infection affecting a resident of the region.” The institute told CNN by telephone on Monday that it was not commenting on the incident.

US Secretary of State Marco Rubio called on Russia to disclose more information about the researcher’s death. “I think it’s incumbent upon Russia to obviously share more information with the world,” Rubio said Tuesday.

“Maybe it’s bigger than we thought. We don’t know, but I think it would be reckless at this moment, given the limited information we still have, to speculate,” Rubio said. He added, “We’re watching it very closely, hour by hour.”

President Donald Trump said Monday that the United States would be willing to assist. “Anybody that has that kind of a problem, we’re always willing to help,” Trump told reporters before leaving the White House for Nebraska.

Regional authorities are carrying out what Maxim Modin, mayor of the Shelekhovsky district, described as a comprehensive set of measures against an epidemic. Shelekhovsky is in eastern Russia near the Mongolian border.

The inpatient facility where the researcher received treatment has been quarantined. Several departments stopped admitting or discharging patients, while local media reported that other hospitals in the region had also closed.

Irkutsk authorities canceled an annual community clean up event that had been scheduled for the weekend. Local media linked that decision to the incident, and officials confirmed the woman’s death last week.

Unofficial accounts, including reporting from the independent regional outlet Liudi Baikala, said nearly 200 people were under observation. Rospotrebnadzor said several people who had contact with the researcher were diagnosed with Covid-19 and rhinovirus, according to state news agency TASS.

Residents described unease even without obvious changes in the city. Ekaterina, a Shelekhov resident, said her acquaintances were “slightly panicking,” while another resident who requested anonymity said he was “shocked.”

The Kremlin urged the public to rely on official information rather than rumors. Kremlin spokesman Dmitry Peskov said people should depend on statements from Rospotrebnadzor.

The World Health Organization told CNN it was communicating with Russian health authorities to verify the event, its circumstances and laboratory testing. “Based on unofficial information available, the public health risk to the general population appears to be low,” it said.

Several regional countries nevertheless introduced precautions. Kazakhstan implemented sanitary and quarantine controls at border crossings, Uzbekistan increased readiness for highly infectious diseases, and Kyrgyzstan announced quarantine controls at state border crossings.

Siberian virologist Alexander Chepurnov said the strict protocols were intended to prevent further spread after suspected exposure. They include immediate reporting, decontamination, medical assessment and isolation in a dedicated facility for as long as someone might remain infectious.

Angela Rassmussen, a virologist at the Vaccine and Infectious Disease Organization, said pneumonic plague is deadly but not highly transmissible. She said illness would require exposure to a high bacterial load and noted that plague is endemic among wildlife in parts of Siberia.

The institute employs about 95 researchers and monitors high risk bacterial and viral infections across Siberia and Russia’s Far East. Pneumonic plague can cause rapidly developing pneumonia, but the World Health Organization says plague is easily treated with antibiotics when detected early.