CARACAS, Venezuela (AP) — Some U.S. diplomats in Venezuela headed for the Caracas airport early Friday amid a political power struggle between President Nicolas Maduro and an opposition leader who has declared himself interim president.

A letter by a U.S. Embassy security officer requesting a police escort for a caravan of 10 vehicles was leaked earlier in the day and published on social media by a journalist for state-owned TV network Telesur. Its authenticity was confirmed by a U.S. official, who spoke on condition of anonymity to discuss sensitive security arrangements.

A defiant Maduro called home all Venezuelan diplomats from the U.S. and closed its embassy in Washington on Thursday, a day after ordering all U.S. diplomats out of the country by the weekend. That followed President Donald Trump's decision to support the claim to power by opposition leader Juan Guaido.

Washington has refused to comply with Maduro's order but has ordered its nonessential staff to leave the tumultuous country, citing security concerns. The Trump administration said Maduro's order isn't legal because the U.S. no longer recognizes him as Venezuela's legitimate leader.

"They believe they have a colonial hold in Venezuela, where they decide what they want to do," Maduro said in an address broadcast live on state TV. "You must fulfill my order from the government of Venezuela."

The diplomats were likely to leave Caracas around midday on one of two daily flights to Miami by American Airlines, the last-remaining U.S. carrier to serve Venezuela after Delta and United Airlines pulled out in 2017 amid a political crisis that has forced millions to flee the country.

Backed by Venezuela's military, Maduro has refused to show any hint he's ready to cede power, setting up a potentially explosive struggle.

Guaido is expected to show up for a news conference later Friday in Caracas amid speculation he could be arrested. The 35-year-old lawmaker's whereabouts have been a mystery since he was symbolically sworn in Wednesday before tens of thousands of cheering supporters, promising to uphold the constitution and rid Venezuela of Maduro's dictatorship.

Speaking from an undisclosed location, Guaido told Univision he would consider granting amnesty to Maduro and his allies if they helped return Venezuela to democracy.

"Amnesty is on the table," said Guaido, who just weeks earlier was named head of the opposition-controlled congress. "Those guarantees are for all those who are willing to side with the constitution to recover the constitutional order."

Besides the U.S., Canada, much of Latin America and many countries in Europe threw their support behind Guaido. Trump promised to use the "full weight" of U.S. economic and diplomatic power to push for the restoration of Venezuela's democracy.

Maduro has been increasingly accused of undemocratic behavior by his opponents and has presided over skyrocketing inflation, a collapsing economy and widespread shortages of basic goods.

Russia, China, Iran, Syria, Cuba and Turkey have voiced their backing for Maduro's government.

China's Foreign Ministry called on the U.S. to stay out of the crisis, while Russia's deputy foreign minister warned the U.S. against any military intervention in Venezuela. Alexei Pushkov, chairman of the information committee at the Russian Federation Council, called Guaido's declaration "an attempted coup" backed by the U.S.

Russia has been propping up Maduro with arms and loans. Maduro visited Moscow in December, seeking Russia's political and financial support. Over the last decade, China has given Venezuela $65 billion in loans, cash and investment. Venezuela owes more than $20 billion.

At an emergency meeting Thursday, 16 nations from the Organization of American States recognized Guaido as interim president.

Attention was focused on Venezuela's military, a traditional arbiter of political disputes in the country, as a critical indicator of whether the opposition will succeed in setting up a new government.

Venezuela's military brass pledged unwavering support to Maduro, delivering vows of loyalty Thursday before rows of green-uniformed officers on state television.

A half-dozen generals belonging largely to district commands and with direct control over thousands of troops joined Maduro in accusing Washington of meddling in Venezuela's affairs and said they would uphold the socialist leader's rule.

Defense Minister Vladimir Padrino Lopez, a key Maduro ally, dismissed efforts to install a "de-facto parallel government" as tantamount to a coup.

"It's not a war between Venezuelans that will solve our problems," he said. "It's dialogue."

Guaido's father, who has lived in Spain for the last 16 years, has called on the military to drop its allegiance to Maduro.

Wilmer Guaido, a taxi driver on the island of Tenerife, told private Antena 3 television Friday that Venezuela's armed forces should be loyal to the country, but not to a specific leader.

"(Simon) Bolivar used to curse against soldiers who give their back to the people," Guaido said, referring to Venezuela's independence hero. "I think the military should choose the right side of history."

Juan Guaido has said he needs the backing of three key groups: The people, the international community and the military. While Thursday's protest drew tens of thousands to the streets and over a dozen nations in the region pledged support, the military's backing is crucial.

Although many rank-and-file troops suffer the same hardships as countless other Venezuelans when it comes to basic needs like feeding their families, Maduro has worked to cement their support with bonuses and other special benefits.

In a video earlier this week, Guaido said the constitution requires the military to disavow Maduro after his May 2018 re-election, which was widely condemned by the international community because his main opponents were banned from running.

But there were no signs that security forces were widely heeding Guaido's call to go easy on demonstrators.

Gunfire during the protests and looting left 21 dead between Wednesday and early Thursday in the capital of Caracas and throughout the country, according to Marco Ponce, coordinator of the nonprofit Venezuelan Observatory of Social Conflict.

U.N. human rights chief Michelle Bachelet called for independent investigations into the violence linked to protests. Her office in Geneva said she "urged all sides to conduct immediate talks to defuse the increasingly incendiary atmosphere."

Many Venezuelans are awaiting Guaido's guidance on the often-beleaguered opposition's next steps.

A virtually unknown lawmaker at the start of the year, Guaido has reignited opposition hopes by taking a rebellious tack amid Venezuela's crushing economic crisis. He escalated his campaign Wednesday by declaring the constitution gives him, as president of the congress, the authority to take over as interim president and form a transitional government until he calls new elections.

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Christine Armario reported from Bogota, Colombia. Associated Press writer Fabiola Sanchez in Caracas contributed.