A laboratory worker at a plague research institute in Russia's Irkutsk region died following an illness, prompting U.S. President Donald Trump to offer American assistance and the World Health Organization to assess the situation as low risk to the public.

Trump told reporters at the White House on Monday that the U.S. would help Russia with the case. "Everybody who has that kind of a problem, we'll always help," he said, describing plague as a "rough disease" that "we used to be able to control." Trump added that "somehow those microbes have gotten stronger and stronger, they're like an army."

The worker fell ill and died in undisclosed circumstances at the anti-plague research institute. Russian authorities quarantined nearly 200 people following the death, according to reporting on the incident.

Trump said he had not spoken to Russian officials about the case. It remains unclear whether Moscow has sought or would accept any assistance from the U.S.

A State Department spokesperson told CNBC the U.S. was "monitoring the situation closely with the CDC and our other interagency partners." The spokesperson said many details had not been confirmed and urged 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 remained underway. The WHO said it was in contact with Russian authorities and had offered support if needed. The organization assessed the risk to the general public as low based on available information. The WHO noted the cause of death had not been confirmed.

It remains unclear whether Russia will disclose further details about the incident or accept external assistance.