In this file photo, Iranian Foreign Minister Mohammad Javad Zarif speaks at the Raisina Dialogue 2020 in New Delhi, India on Jan 15, 2020. (MANISH SWARUP / AP)

TEHRAN - Iran complained to the United Nations on Sunday and summoned the Swiss ambassador in Tehran, who represents US interests in the Islamic Republic, over possible measures Washington could take against an Iranian fuel shipment to Venezuela.

The oil sectors of Iran and Venezuela, members of OPEC, are both under US sanctions. The Trump administration official declined to specify the measures being weighed but said options would be presented to Trump

A senior official in US President Donald Trump’s administration told Reuters on Thursday the United States was considering measures it could take in response to Iran’s shipment of fuel to crisis-stricken Venezuela.

The oil sectors of Iran and Venezuela, members of OPEC, are both under U.S. sanctions. The Trump administration official declined to specify the measures being weighed but said options would be presented to Trump.

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Iran’s Deputy Foreign Minister Abbas Araqchi passed on a message to the Swiss ambassador on Sunday warning against any US threat against the Iranian tankers, according to a report on the foreign ministry website.

Araqchi also said that any threat against his country's tankers will elicit Iran's "immediate and categorical reaction, and the US administration will be responsible for their consequences."

Iranian Foreign Minister Mohammad Javad Zarif also wrote a letter to UN Secretary-General Antonio Guterres.

Iran “reserves its right to take all appropriate and necessary measures and decisive action ... to secure its legitimate rights and interests against such bullying policies and unlawful practices,” Zarif wrote to Guterres.

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“This hegemonic gunboat diplomacy seriously threatens freedom of international commerce and navigation and the free flow of energy,” Zarif wrote. “These efforts by the US to take coercive measures to disrupt Iran’s oil sale is a dangerous escalation.”

"The United States must stop acting as a bully at the international level and respect the rule of international laws, in particular the right to free shipping in free waters," he added.

At least one tanker carrying fuel loaded at an Iranian port has set sail for Venezuela, according to vessel tracking data from Refinitiv Eikon on Wednesday, which could help ease an acute scarcity of gasoline in the South American country.

Venezuela is in desperate need of gasoline and other refined fuel products to keep the country functioning amid an economic collapse under socialist President Nicolas Maduro. Venezuela produces crude oil but its infrastructure has been crippled during the economic crisis.

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On Saturday, Hamid Hosseini, the spokesman for the Iranian Association of Exports of Crude Products, said that the United States would practically be unable to block shipments of fuel from Iran to Venezuela at a time when the two countries need to cooperate to mitigate the impact of American sanctions on their energy sectors.

"Gasoline shipment is not one that could be intercepted or attacked," Hosseini said. "It would be a remote possibility for the US to block the gasoline export shipment," he added.

He described Iran's decision to ship large consignments of gasoline to Venezuela as a right move meant to help Caracas tackle its fuel shortage.

He also said Iran should continue to export more of such shipments in the future to offset a reduction in domestic demand as a result of the coronavirus pandemic.

Western media also reported earlier that Venezuelan government officials piled a large sum of gold, reportedly worth US$500 million, on Tehran-bound jets in April as payment for Iran's assistance in reviving Venezuela's gasoline refineries. 

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On May 11, the Iranian ambassador to Caracas, Hojjatollah Soltani, denied that his country had received gold bars from Venezuela.

He said reports claiming that Venezuela was raiding its gold vaults and handing tons of bars to Iran through recent Mahan Air flights were a "big lie" and "baseless".

In recent days, commercial flights had been made from Iran to Venezuela for the transfer of equipment to reactivate the Paraguana Refinery Complex, Soltani said.

"The Iranian government's cooperation with Venezuela has expanded in the time of novel coronavirus crisis, and our relations, especially in the area of trade cooperation, are stronger than ever," he added.