WICHITA, Kansas (Reuters) - The FBI is investigating possible threats to the water supply systems in Wichita, Kansas, and several other Midwestern cities that are as yet unsubstantiated, a spokeswoman said on Friday.

The U.S. Federal Bureau of Investigation learned of the threats in the past two days and has contacted the water supply facilities and law enforcement offices for the municipalities, said Bridget Patton, a spokeswoman for the FBI office in Kansas City, Missouri.

Patton declined to discuss the nature of the threats or the number of cities affected. She said investigators had been sent out in response to the reports, but offered no details.

“We were made aware of the threat,” Patton said. “We have not been able to substantiate any of the threats.”

Wichita city officials warned employees in emails to be on guard for suspicious activities. City officials also told residents the water is safe to drink and the public will be notified immediately if this changes.

Wichita Police Lieutenant Doug Nolte said Friday that the city had taken steps to keep the city’s water supply safe, but would not describe what measures had been taken.

Wichita draws much of its water from the Cheney Reservoir about 30 miles west of the city. The city water department has not returned calls regarding security measurements taken.