ISTANBUL (Reuters) - The United States is monitoring trade between its NATO ally Turkey and Venezuela and will take action if it judges any sanctions have been violated, a senior U.S. official said on Thursday.

Supporters of Venezuelan opposition leader and self-proclaimed interim president Juan Guaido take part in a protest against Venezuelan President Nicolas Maduro's government in Caracas, Venezuela January 30, 2019. REUTERS/Andres Martinez Casares

Three months ago Washington introduced new sanctions aimed at disrupting gold sales from Venezuela, which exported more than 20 tonnes of the precious metal to Turkey in 2018.

On Friday Marshall Billingslea, U.S. assistant secretary for terrorist financing at the Treasury, is due to hold talks in Ankara with the Turkish government.

The trip was originally planned to discuss U.S. sanctions on Iran, which exports gas to neighboring Turkey, but was likely to include Venezuelan issues as well, a senior U.S. official said.

“We are looking at the nature of Turkish-Venezuelan commercial activity, and if we assess a violation of our sanctions, we will obviously take action,” the official said.

Last year Venezuela exported 23.63 tonnes of gold worth $900 million to Turkey, compared to zero the year before, official Turkish data showed. Nearly all that quantity was in the first nine months of the year, before Washington imposed new sanctions in November.

Turkey’s President Tayyip Erdogan has stood by his Venezuelan counterpart Nicolas Maduro, calling him last week to express support after Washington backed opposition leader Juan Guaido as interim head of the country.

The official said Washington was disappointed that Turkey continued to support Maduro.

“We have talked to the Turks like we have talked to an awful lot of governments around the world, sharing our perspective and asking them to join us in acknowledging the illegitimacy of the Maduro regime,” the official said.

“They have not responded positively to that conversation thus far.”