According to Mandelker, Washington has raised concerns over an alleged illicit shipment of Iranian oil with Malaysia and Singapore.
On Tuesday, the US Department of the Treasury sanctioned 25 Middle Eastern entities and individuals over their alleged involvement in trading and funding Iran’s Islamic Revolutionary Guard Corps (IRGC) and other Iranian military units.
The Treasury Department explained that the IRGC-controlled Ansar Bank and the bank’s currency exchange arm served as the hub for a regional network with layers of intermediary entities allowing devalued Iranian rials to be exchanged for dollars and euros.
The US sanctions against Tehran were reinstated last year after the United States withdrew from the Iran nuclear deal, which envisaged the relief of economic sanctions against Tehran in return for Iran's pledge to keep its nuclear programme peaceful.
In early November, Washington granted six-month waivers from oil sanctions on Tehran to eight countries that are dependent on Iranian energy imports.
Last month, US Special Representative for Iran Brian Hook said that the United States, however, wanted to get to zero imports of Iranian oil as soon as possible and, therefore, would not provide exemptions from sanctions for companies and countries that are involved in cooperation with Iran.
Meanwhile, Mandelker also said Friday, cited by Reuters, that Washington would bring "maximum pressure" on the government of Venezuelan President Nicolas Maduro.
Russia, China, Mexico, among other nations, have voiced support for constitutionally elected Maduro, who, in turn, has accused Washington of orchestrating an attempted coup with Guaido's help.
The US Treasury has since January imposed several rounds of sanctions on Venezuelan state companies, such as PDVSA. US National Security Advisor John Bolton said last week that Washington has yet to impose its toughest sanctions against the government of Maduro.