KANSAS CITY, Mo. (AP) — Federal investigators say they’ve been alerted about a small number of men suspiciously buying dozens of prepaid, disposable cellphones from Walmart stores in three Missouri cities.

The purchases last weekend in Columbia, Lebanon and Macon raised red flags because such cell phones, often called “burners,” frequently are discarded in an effort to avoid detection. And such phones can be used as bomb detonators.

It’s not clear if the same men are suspected of making all of the questioned purchases. But two who bought roughly 60 phones early last Saturday in southwestern Missouri’s Lebanon were questioned by police and released.

An FBI spokeswoman, Bridget Patton, says it’s not uncommon that local law enforcers contact that agency if they deem something suspicious. But Patton isn’t saying if the FBI is formally investigating.