President Donald Trump offered U.S. assistance to Russia after a laboratory worker died at a plague research institute in the Irkutsk region of eastern Siberia, though it remains unclear whether Moscow has sought or would accept help.

Trump told reporters at the White House on Monday that "we'll help" and described plague as a "rough disease" that "we used to be able to control." He noted that "somehow those microbes have gotten stronger and stronger, they're like an army." Trump said he had not spoken to Russian officials about the case.

The laboratory worker fell ill and died in undisclosed circumstances at the anti-plague research institute, according to Reuters. Russian authorities quarantined nearly 200 people in response, prompting public health concerns.

A U.S. State Department spokesperson told CNBC that the department is "monitoring the situation closely with the CDC and our other interagency partners" but that "many details have not been confirmed." The department encouraged Russian authorities to "share accurate information quickly and openly."

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

Russian authorities said the situation was under control, but have not publicly disclosed the circumstances of the worker's death or confirmed the cause.

Trump previously stated that he considers Russian President Vladimir Putin someone he can work with, despite ongoing tensions over Moscow's war in Ukraine.