I found this somewhere on the endless stretch of the Internets, namely the website All Empires:

Quote Originally Posted by Cyrus Shahmiri
This is part of the inscription of Sargon II in the Palace of Khorsabad:

21. I attacked and conquered KIBABA, Prefect of the town of Kharkhar, I took him and the inhabitants of his country captive, I rebuilt this city and made the inhabitants of the provinces, that my arm had conquered, live there. I placed my Lieutenant as Governor over them. I named the town Kar-Sarkin j I established the worship of the god ASSUR, my Master, there. I erected an image of my Royal self. I occupied 6 towns in the environs, and added them to his government.
22. I besieged and took the towns of Tel-Akhi-tub, Khindau, Bagai, and Anzaria; I transported the inhabitants of them to Assyria. I rebuilt them; I gave them the names of Kar-Nabu, Kar-Sin, Kar-Ben, and Kar-Istar.
23. To maintain my position in Media, I have erected fortifications in the neighbourhood of Kar-Sarkin. I occupied 34 towns in Media and annexed them to Assyria and I levied annual tributes of horses upon them.
24. I besieged and took the town of Eristana, and the surrounding towns in the country of Bait-Ili ; I carried away the spoil.
I think Kharkhar is the same Khalkhal, a large city in the north west of Iran, Bagai should be Baga (modern Baku) capital of Azerbaijan, Anzaria seems to be Anzali, the largest Iranian port on the western shore of the Caspian Sea and Eristana is modern Heris/Heristan in the east of Tabriz.

There are several towns called, or once called, Kharkhar, and all of them are in Iran, as far as I know. Some are far closer to Sargon's heartland of Assyria than the Kharkhar in this map, but still -- did the Assyrians really penetrate this deeply into the Iranian plateaux? Or anywhere near this far?