The Communications Regulator is warning consumers to be careful about returning apparent missed calls on their mobile phones.
The warning comes in the wake of a phone scam, which emerged over the weekend, targeting thousands of Irish mobile phone users.
They received missed calls that appeared to be from an 086 number, but when they returned the call they were connected to a premium rate service that appears to be based in Slovenia.
It appears that only 087 numbers were targeted.
There have been reports that the number redirects to a premium sex line.
Anyone who believes they have fallen victim is advised to contact their phone provider to see what, if any, charges they have incurred.
Speaking on RTÉ's Morning Ireland, Retail and Consumer Services Director at ComReg Barbara Delaney said phoning the number could be costly.
She said: "The reason it's a missed call is because it's not long enough to answer, so it's purposely missed.
"It appears on your phone with the missed number beginning with +386 so people think it's an Irish number and are then inclined to call it back ... that's where the charge would apply.
"We would urge people to be vigilant in this respect for two reasons.
"Firstly, because you may get it at a time when you might not be expecting a call and, secondly, because of the digits it commences with you may be caught off guard and think it is an Irish mobile number.
"So we would urge consumers not to call back numbers that they don't know where it came from."