The U.S. is closely monitoring the death of a Russian lab technician

President Donald Trump said the United States was watching "very closely" the death of a Russian laboratory technician at a plague research center in Siberia.

Secretary of State Marco Rubio said that Washington is closely watching developments and is worried that the incident may lead to the spread of pneumonic plague, but there is currently no reason to panic.

The governor of Irkutsk, Russia, called the cause of death "pneumonia of unknown etiology" and said that "no microorganisms related to the woman's work were found in the biological samples of the deceased."

Unconfirmed reports suggest that the woman fell ill after breaking a test tube containing the pathogen, or she may have become ill after a field trip to an area where plague is naturally endemic among wild rodents.

Asked how Washington would respond to the risk of the pandemic spreading from Russia, Trump said he had not yet communicated with the Kremlin about it.

"I'm sorry to see them in this situation," Trump said, adding: "We're going to help. Anyone who has a problem like this, we're going to try to help."

Irkutsk Governor Igor Kobzev cited a statement from Russia's consumer rights and health watchdog (Rospotrebnadzor) as saying there had been no reports of other staff from the plague institute seeking medical attention since the death of the laboratory technician.

The regulator also said biosecurity teams had inspected the Siberian and Far Eastern Plague Prevention Institute in Irkutsk and found no emergency.

In response, Kremlin spokesman Dmitry Peskov urged people not to "listen to rumors" but to "believe the official statement of the Russian Service for Supervision of Consumer Rights Protection and Welfare."

Russian media reported last week that nearly 200 people known to have been in contact with the deceased were under medical observation as a precaution.

Asked by reporters for "an update on suspected plague cases in Russia," Rubio said: "It appears that a worker in the laboratory was infected and there is concern that this could spread, at least internally - you've seen them take quarantine actions."

"If this type of virus spreads, it can spread very quickly. So we are watching and monitoring closely. I don't think it is something to panic about, but it does require us to pay attention and pay close attention to it, and we are doing that."

According to Russian media reports, the deceased woman was named Daria, who was nearly 30 years old. She had recently visited the Buryatia region bordering Mongolia.

The bacterium Yersinia pestis killed half of Europe's population in the 14th century and was known as the Black Death. The bacterium has recently been found in rodents in the region, such as prairie dogs.

More than 100 years ago, the Anti-Plague Institute of Siberia and the Far East was established in response to an outbreak of plague in the 1920s.

Dr Simon Clarke, associate professor of cellular microbiology at the University of Reading, told BBC Radio 4 that pneumonic plague, caused by the Yersinia pestis virus, is almost always fatal if left untreated, but can be treated with antibiotics.

"Pneumonic plague can be spread through person-to-person contact, which is why people are worried about it," he said.

He added: "But of course, when people think about infectious disease outbreaks, the first thing that comes to mind is... lockdowns and COVID-19, and that just doesn't happen here."

"People think: Oh! The plague is over, it passed hundreds of years ago, but that's not the case," Clark said.

"It's still out there and in some parts of the world it's a risk to human health, which is why they need to study it."