A nine-year-old girl ran home from near the Creggan Library after three men asked her to get into a white van on Wednesday afternoon.
Chief Inspector Tony Callaghan said police were trying to establish the circumstances of the incident and are appealing for information.
“The young girl did exactly the right thing in running home and alerting her parents,” he said.
At around 4.15pm on Wednesday, the nine-year-old girl was in the area of the Creggan library when the white van stopped near her.
One of three men in the van asked her to get in, but she refused and ran home.
Police can be contacted on the 101 non-emergency number.