ISTANBUL, Feb 4 (AFP) - The United States warned Turkey in recent days about the export to Russia of chemicals, microchips and other products that can be used in Moscow's war effort in Ukraine, and it could move to punish Turkish companies or banks contravening sanctions.

Brian Nelson, the U.S. Treasury Department's top sanctions official, visited Turkish government and private sector officials on Thursday and Friday to urge more cooperation in disrupting the flow of such goods.

In a speech to bankers, Nelson said a marked year-long rise in exports to Russia leaves Turkish entities "particularly vulnerable to reputational and sanctions risks", or lost access to G7 markets.

They should "take extra precaution to avoid transactions related to potential dual-use technology transfers that could be used by the Russian military-industrial complex," he said in a copy of the speech issued by the Treasury.

In the meetings in Ankara and Istanbul, Nelson and a delegation highlighted tens of millions of dollars of exports to Russia that raised concerns, according to a senior U.S. official who requested anonymity.

"There is no surprise...that Russia is actively looking to leverage the historic economic ties it has in Turkey," the official said. "The question is what is the Turkish response going to be."

NATO member Ankara opposes the sweeping sanctions on Russia on principle but says they will not be circumvented in Turkey, urging the West to provide any evidence.

Western nations applied the export controls and sanctions after Moscow's invasion nearly a year ago. Yet supply channels have remained open from Hong Kong, Turkey and other trading hubs.

Citing Russian customs records, Reuters reported in December that at least $2.6 billion of computer and other electronic components flowed into Russia in the seven months to Oct. 31. At least $777 million of these products were made by Western firms whose chips have been found in Russian weapons systems.