Reuters - The first of five Iranian tankers carrying fuel for gasoline-starved Venezuela entered the South American country�s exclusive economic zone on Saturday, despite a U.S. official�s warning that Washington was considering a response to the shipment.

The tanker, named Fortune, reached the country�s waters at around 7:40 p.m. local time (1140 GMT) after passing north of the neighboring dual-island Caribbean nation of Trinidad and Tobago, according to vessel tracking data from Refinitiv Eikon.

�The ships from the fraternal Islamic Republic of Iran are now in our exclusive economic zone,� tweeted Tareck El Aissami, Venezuela�s economy vice president and recently named oil minister.

Venezuelan state television showed images of a navy ship and aircraft preparing to meet it. The defense minister had pledged that the military would escort the tankers once they reached Venezuela�s Exclusive Economic Zone (EEZ) due to what authorities described as threats from the United States.

The tanker flotilla is carrying a total of 1.53 million barrels of gasoline and alkylate to Venezuela, according to both governments, sources and calculations by TankerTrackers.com.

The desperately needed shipments have caused a diplomatic standoff between the United States and Iran and Venezuela, which are under U.S. sanctions. Gasoline is scarce in Venezuela due to a near-complete breakdown of the OPEC nation�s 1.3 million barrel-per-day refining network.

Washington is considering measures in response, a senior U.S. official said without elaborating.

The United States recently beefed up its naval presence in the Caribbean for what it called an expanded antidrug operation. A Pentagon spokesman said on Thursday he was unaware of any operations related to the Iranian cargoes.

The shipment has drawn condemnation from Venezuela�s opposition, which is concerned about growing ties between Iran and socialist President Nicolas Maduro, who has overseen a six-year economic crisis. The shipments are bringing enough fuel for just a month of consumption at current rates in the nation, once a prominent fuel exporter.

�(The ruling party) is trying to turn an embarrassment into an epic victory,� said Oscar Ronderos, a lawmaker on the opposition-controlled National Assembly�s energy commission.

Earlier on Saturday, Iranian President Hassan Rouhani warned of retaliation if Washington caused problems for tankers carrying Iranian fuel to Venezuela, the semi-official news agency Mehr reported.

�If our tankers in the Caribbean or anywhere in the world face trouble caused by the Americans, they (the U.S.) will also be in trouble,� Rouhani said in a telephone conversation with Qatar�s Emir, Mehr reported.

The two OPEC nations have previously helped each other in the face of U.S. sanctions. In 2010-2011, state-run oil company PDVSA [PDVSA.UL] sent fuel to Iran, which was under sanctions aimed at stifling its nuclear weapons program.

Reporting by Dubai newsroom, Deisy Buitrago in Caracas, Luc Cohen in New York and Marianna Parraga in Mexico City; Editing by David Evans, Jonathan Oatis, Sonya Hepinstall and Richard Chang