A 28-year-old Russian scientist has died after a test-tube incident at the country's anti-plague institute in Irkutsk.

Daria Shipilova was working with a sample at the institute when the accident happened. Russian authorities described her illness as a pneumonia of unknown origin.

About 200 of her contacts have been placed under medical observation. Quarantine measures were imposed around the institute and her recent movements are being traced.

The White House said it was monitoring the situation. President Donald Trump offered American assistance to Moscow, an offer Russian officials have not publicly accepted.

The Irkutsk institute is one of Russia's main facilities for studying plague and other dangerous pathogens. Its work dates back to the Soviet era.

Health experts say the key question is whether anyone else falls ill. So far officials have reported no confirmed secondary cases.

Plague is caused by the bacterium Yersinia pestis and is treatable with antibiotics if caught early. Russian health officials have not reported any wider outbreak linked to the incident.

Sources: nypost.com, thetimes.com, usatoday.com.