By MATTHEW LEE and BEN FOX, Associated Press

WASHINGTON (AP) — The Trump administration quickly declared enthusiastic support Tuesday for the Venezuelan opposition effort to spark a military uprising against embattled President Nicolas Maduro, hoping for decisive action in the political crisis that has engulfed the South American nation.

Late in the day, President Donald Trump threatened a "full and complete embargo" and sanctions on Cuba if its troops do not cease operations in Venezuela. National security adviser John Bolton alleged earlier that Cuban troops were keeping Maduro in power in Caracas.

Cuban President Miguel Diaz-Canel rejected Trump's threat with a tweet of his own. "We vigorously reject Trump's threat of a complete and total blockade against Cuba. There are no Cuban military operations or troops in Venezuela ... Enough lies, already."

Trump and senior foreign policy figures in his administration all weighed in during the day, casting the effort headed by opposition leaders Juan Guaido and Leopoldo Lopez as a move to restore democracy, not an attempted coup like the short-lived effort to oust then-President Hugo Chavez in 2002 that seemed to have U.S. support.

"We are with you!" Vice President Mike Pence tweeted to the opposition. Pence, who has had a lead role in the administration's effort to persuade Maduro to give up power, told the opposition group, "America will stand with you until freedom & democracy are restored."

Likewise Trump himself tweeted that he was monitoring the situation and "the United States stands with the people of Venezuela and their Freedom!"

Lopez, the country's most prominent opposition activist, had been under house arrest, and his sudden appearance would seem to have required the cooperation of troops who guard him. However, late Tuesday, he sought refuge with his family in the Chilean Embassy in Caracas, a discouraging sign for supporters of the uprising.

Bolton said it was a "very delicate moment" for Venezuela.

"If this effort fails, they will sink into a dictatorship from which there are very few possible alternatives," he said at the White House.

The wholehearted embrace of the rebellion reflects the goals of an administration that from its earliest days has sought the removal of Maduro. But it was also an unusually full-throated endorsement by any government for a mass protest that was turning violent.

"It's more than cheerleading. They are very actively collaborating," said Mark Weisbrot, who is co-director of the Center for Economic and Policy Research in Washington and has called for a negotiated end to the political crisis.

The U.S. and about 50 other nations take the position that Maduro's re-election last year was irrevocably marred by fraud and he is not the legitimate president of Venezuela, a once prosperous nation that has the world's largest proven oil reserves.

In January, the administration took the unusual step of recognizing Guaido, the opposition leader of the National Assembly, as interim president. It also imposed punishing sanctions on Venezuela's oil sector, deepening the country's economic crisis.

Despite these and other measures, Maduro, the hand-picked successor to Chavez, has retained his hold on the country and the support of the security services.

That support had seemed to crack Tuesday with the launch of what the opposition was calling "Operation Freedom," which began with the early-morning release of a short video of Guaido and Lopez alongside a few dozen national guardsmen urging people to "take to the streets."

"What we are seeing today in Venezuela is the will of the people to peacefully change the course of their country from one of despair to one of freedom and democracy," Secretary of State Mike Pompeo tweeted in an early reaction. "The U.S. stands with them."

Pompeo said in media interviews and in a speech Tuesday that Maduro was on the verge of flying out of the country before the Russians persuaded him to stay. Pompeo provided no evidence for the assertion, which Maduro himself ridiculed. "Mr. Pompeo, what lack of seriousness," Maduro said.

The Trump administration was caught slightly off-guard by Guaido's decision to launch the campaign on Tuesday. Elliott Abrams, the special representative for Venezuela, said the administration had expected major marches and protests to take place on Wednesday for the May Day holiday.

At some point after that, Abrams said, U.S. officials had been led to believe that the chief judge of Venezuela's Supreme Court, the defense minister and the chief of the presidential guard would declare their support for the constitution and, by extension, renounce Maduro's leadership. Abrams said U.S. officials believed such a step would galvanize public support for Guaido.

"What was going to happen, we were told, was that they would announce their support for the constitution," he told reporters at the State Department.

That did not occur and Abrams said "the situation on the ground remains confused." Nonetheless, Abrams said he had been in contact with Guaido by text message at midafternoon and the opposition leader seemed "buoyant and determined."

Bolton said a peaceful transfer of power from Maduro to Guaido could still occur if "enough figures depart from the regime and support the opposition."

He and others in the administration also called on Cuba and Russia to withdraw support. The U.S. has said about 20,000 Cubans provide security assistance to the Maduro government. Cuba denies that and says most of those people are medical workers.

The U.S. has been embarrassed by acting too soon in the past. In April 2002, a businessman who had repeated meetings with American officials staged a coup against Chavez. While other countries in the hemisphere denounced the move, the administration of then President George W. Bush acknowledged the new government. It had to backtrack as the rebellion fizzled.

Trump administration officials sought to draw a distinction between the two situations. Acting White House chief of staff Mick Mulvaney, at a conference in California, said the U.S. considers Guaido, not Maduro, the legitimate leader of the country under the Venezuelan constitution. "Importantly, we do not consider it a coup," he said.

Still, Abrams sounded uncertain as to how Guaido's bid would end and appeared to set the stage for his possible defeat.

"We know this: At the end of the day, Juan Guaido will still be the legitimate interim president of Venezuela, the United States will still be supporting him," he said. "The Maduro regime, while it exists, will still be illegitimate and completely incapable of solving the problems of the Venezuelan people."