A gas flare on an oil production platform in the Soroush oil fields is seen alongside an Iranian flag in the Gulf.

The United States is keen to see that Malaysia, Singapore and others are fully aware of illicit Iranian oil shipments and the tactics Iran uses to evade sanctions, a top U.S. sanctions official said on Friday.

Sigal Mandelker, under-secretary of the Treasury for Terrorism and Financial Intelligence, told reporters in Singapore the United States had placed additional "intense pressure" on Iran this week.

"It's very important that these countries have important visibility into the different ways the Iranian regime uses to deceive the international community in connection with shipment of oil," she said, referring to her talks in Singapore and Malaysia.

She said would stress the inherent risks in dealing with Iran in meetings over coming days with government officials in Malaysia, Singapore and India.

"This trip follows on the heels of additional intense pressure we have placed on Iran. In just the last week, we took action against nuclear scientists and agencies and other key personnel involved with the Iranian regime's past nuclear weapons entities," Mandelker said.

"We are making them radioactive to the international community."

Action had been taken this week against a network involved in an Iranian sanctions evasion scheme — a network that includes Iran-, UAE- and Turkey-based front companies, she said.

Mandelker said she was due to meet Singapore's home, finance and trade ministries on Friday. She met officials at its central bank on Thursday.

She said the United States was also bringing "maximum pressure" on the Venezuelan government of President Nicolas Maduro.

