Trump offered U.S. assistance to Russia after a laboratory worker died at an anti-plague research institute in the Irkutsk region of eastern Siberia. The worker fell ill and died in undisclosed circumstances, prompting authorities to quarantine nearly 200 people.

"We'll help," Trump told reporters at the White House on Monday. "Everybody who has that kind of a problem, we'll always help." Trump said he had not spoken to Russian officials about the case but described plague as a "rough disease" and noted that "somehow those microbes have gotten stronger and stronger, they're like an army."

A State Department spokesperson told CNBC the U.S. was "monitoring the situation closely with the CDC and our other interagency partners" but added that "many details have not been confirmed." The statement urged Russian authorities to "share accurate information quickly and openly." It remains unclear whether Moscow has sought or would accept assistance.

The World Health Organization said in an email that the cause of death had not been confirmed and testing was underway. WHO stated it was in contact with Russian authorities and had offered support if needed. Based on available information, WHO assessed the risk to the general public as low.

Russian authorities said the situation was under control. Trump previously stated he considers Russian President Vladimir Putin someone he can work with, despite tensions over Moscow's war in Ukraine.