The Federal Communications Commission is sounding the alarm about a new phone scam that could wind up costing you a pretty penny.

Robocalls coming from places such as Mauritania and Sierra Leone take advantage of human curiosity, the Fort Worth Star-Telegram reports. Typically, these incoming calls only ring once. The scammers' aim is to get people wondering who just dialed their number to pick up the phone and return the call.

That's when the fees start adding up. 

“If you call any such number, you risk being connected to a phone number outside the U.S.,” the FCC said in a written statement. “As a result, you may wind up being charged a fee for connecting, along with significant per-minutes fees for as long as they can keep you on the phone. These charges may show up on your bill as premium services.”

Many of the robocalls come from the 222 or 232 area codes, according to the Star-Telegram.

The FCC suggests people don't answer calls from numbers they don't recognize. Also don't return calls unless you know who you're dialing.

Consumers can also contact their cellphone carrier to block all outgoing international calls.