Donald Trump says the US was looking "very strongly" at the case but had not discussed it with the Kremlin

President Donald Trump says the US is looking "very strongly" at the case of a Russian lab technician who died at a plague research centre in Siberia.

Secretary of State Marco Rubio said Washington was watching closely amid concerns the incident could lead to the spread of pneumonic plague, but there was no cause for alarm.

Announcing the cause of death as "pneumonia of undetermined etiology", Irkutsk's governor said "no micro-organisms" linked to the woman's work had been found "in her biological samples".

Unconfirmed reports suggested the woman fell ill either after breaking a test tube containing the pathogen or following a field trip to a region where plague occurs naturally among wild rodents.

Asked what Washington was going to do about the risk of plague spreading from Russia, Trump said he had not spoken to the Kremlin about it.

"I hate to see them having it," he said, but added: "We'll help. Everybody who has that kind of a problem, we'll always help."

No other cases of staff from the plague institute seeking medical attention since the lab technician's death had been reported, Irkutsk governor Igor Kobzev said, quoting Russia's consumer and health watchdog, Rospotrebnadzor.

The watchdog said a biological safety team had inspected the Anti-Plague Institute of Siberia and the Far East in Irkutsk and found no emergency situation there.

Kremlin spokesman Dmitry Peskov urged people not to "listen to various rumours" but "rely on Rospotrebnadzor's official statements" instead.

Russian media reported last week that nearly 200 people known to have had contact with the dead woman were under medical observation as a precaution.

Asked by a reporter for an "update on the suspected plague case in Russia", Secretary of State Marco Rubio said: "It seems that there was a worker at the lab that was infected and there's concern that that, you know, could have spread, at least internally - you've seen them do quarantine of this and that nature.

"If something like that gets out, it can quickly spread. So we're watching and monitoring it closely. I don't think it's cause for alarm, but it is cause for focus and the cause to just keep an eye on it and we're doing that."

The woman who died, whose first name was given by Russian media as Daria and who was in her late twenties, had recently visited the Buryatia region on the border with Mongolia.

The plague bacterium or Yersinia pestis, external, which killed up to half the population of Europe in the 14th Century when it was known as the Black Death, is found among rodents such as marmots in the area.

It was in response to an outbreak in the 1920s that the Anti-Plague Institute of Siberia and the Far East, external was founded just over 100 years ago.

Dr Simon Clarke, an associate professor in cellular microbiology at the University of Reading, told BBC Radio 4's PM programme that the pneumonic version of Yersinia pestis was nearly always fatal if left untreated, but could be overcome with antibiotics.

"Pneumonic plague can transmit from person to person and that is why there is the concern around this," he said.

He added: "But of course people's thought with any outbreak of infectious disease at all runs to... lockdowns and Covid and that is just not what's going to happen here."

"People think, 'Oh the plague, that's gone, that went hundreds of years ago,' but it hasn't," Clarke said.

"It's still around and in certain parts of the world, it's a threat to human health and that's why they need to study it."

Asked if the pathogen might have been studied for potential use as a bio-weapon, the scientist agreed it was possible.

"Because this is Russia people's thoughts are running to that, but I think my earlier explanation is probably more likely," Clarke said.

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