The Federal Communications Commission is warning consumers about a robocall scam that’s been popping up around the country.

The “One Ring” or “Wangiri” scheme has been recently targeting specific area codes in bursts, often calling residents multiple times in the middle of the night, according to the FCC.

The federal agency said the scammers are likely trying to get people to call the number back to rack up expensive per minute toll charges.

Recent reports indicate some of the calls are using the “222” country code of the West African nation of Mauritania, while others used the “232” code from Sierra Leone.

Whatever you do, don’t call the number back.

The FCC explained that the “One Ring” scam typically involves a robocaller calling then hanging up after just a ring or two and possibly calling repeatedly. If you call the number back, it could run up a toll that largely gets back to the scammers, according to the FCC.