iPhone 5S unlocking

Hi, I bought iPhone5S, just now in Duty Free shop. When I put my SIM into it, it says "The SIM card that you currently have installed in this iPhone is from a carrier that is not supported under the activation policy that is currently assigned by the activateion server. This is not a hardware issue with the iPhone. Please insert another SIM card from a supported carrier or request that this iPhone be unlocked by your carrier. Please contact Apple for more information"

I am foreign country and my SIM might not be able to connect any network. But according to the message I am getting from the phone, I feel it is more like the activation problem. Can any body help me and point me to where and who should I contact, or what should I do? I dont' want to cut another SIM card into Nano size and the whole thing still doesn't work.

Thank you in advance for your suggestion.

Bests

Suresh