TEHRAN, May 17 (Xinhua) -- Iranian officials on Sunday warned the United States against any attempt to block the fuel delivery by Iranian tankers to Venezuela.

Iran's Foreign Minister Mohammad Javad Zarif said in a letter to the United Nations Secretary General Antonio Guterres on Sunday that "the illegal, dangerous and provocative U.S. threats" against the Iranian tankers is a form of piracy and a big threat to international peace and security.

"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 said in his letter.

Zarif noted that the U.S. administration would be responsible for the consequences of any "illegal move" in this regard.

Iran preserves the right to adopt appropriate and necessary measures in the face of such threats, he added.

In the day, Iran's Deputy Foreign Minister for Political Affairs Abbas Araqchi summoned the Swiss ambassador, whose country represents U.S. interests in Tehran, to voice Iran's strong protest at what he called U.S. "provocations."

Araqchi urged the Swiss ambassador to convey "the Islamic Republic's serious warnings to the American officials against any possible threat posed by the U.S. to the Iranian oil tankers."

Iran and Venezuela enjoy "completely legitimate and legal trade relations," Araqchi said.

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

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

Washington is extremely angry about Iran's delivery of fuel to a location near its borders despite various sanctions it has imposed on Tehran's shipping and energy sectors, Hosseini was quoted as saying by Press TV.

"Gasoline shipment is not one that could be intercepted or attacked," Hosseini said. "It would be a remote possibility for the U.S. 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 which is 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 for the fuel which has come as a result of the novel coronavirus pandemic.

On Wednesday, Western media reported that "at least one tanker carrying fuel loaded at an Iranian port has set sail for Venezuela ... which could help ease an acute scarcity of gasoline in the South American country."

Accordingly, the White House announced on Thursday the United States was considering measures it could take in response to Iran's shipment of fuel to crisis-stricken Venezuela.

Earlier, western reports also said that the Venezuelan government officials piled large sum of gold, an amount equal to about 500 million U.S. dollars, on Tehran-bound jets in April as payment for Iran's assistance in reviving Venezuela's gasoline refineries.

On May 11, the Iranian ambassador to Caracas, Hojjatollah Soltani, denied that his country had received gold bars from Venezuela in return for its services to the restoration of Venezuelan gasoline refinery.

The news claiming that Venezuela is raiding its gold vaults and handing tonnes of bars to Iran through recent Mahan Air flights is a "big lie" and "baseless" claims, said Soltani.

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," the Iranian ambassador stressed.