The Ukrainian president spoke with ABC News' James Longman on Friday.
Russia said over 200 people had been placed in quarantine.
The State Department said it's officially requested more information.
"Safety and security of U.S. citizens is our highest priority," the CDC said.
Ever since the death of a 28-year-old woman who worked at a research lab in Siberia, fear about the suspected plague that's believed to have killed her has exploded. But a UCSF infectious disease expert says that for now, those fears are overblown and it's "not another COVID."