In the first major action by the government of Venezuelan President Nicolás Maduro to fend off a leadership challenge, the country's Supreme Court on Tuesday barred opposition leader Juan Guaidó from leaving Venezuela and ordered a freeze on his financial assets.

Chief Justice Maikel Moreno said the court was initiating a "preliminary investigation" and the "precautionary measures" against Guaidó were designed to "safeguard the country's integrity." In the spring of 2017, Moreno sparked controversy in Venezuela and around the world when he nullified the powers of the National Assembly after opposition lawmakers gained control of the body through an election. 

The decision by the 32-member tribunal came after Venezuela's attorney general Tarek Saab asked the court, which is stacked with Maduro's allies, to launch a criminal probe against Guaidó, the 35-year-old president of the country's National Assembly. During a press conference outside the court Tuesday, Saab accused Guaidó of leading an "assault against the Venezuelan fatherland," but did not mention any specific crimes he believed the opposition leader had committed.  

Responding to Saab's announcement at a press conference before the court's order, Guaidó said he did not underestimate the threat of imprisonment, but he did not believe it was "anything new." He added the accusations were part of the Maduro regime's pattern of persecution and repression against the Venezuelan people.

The Trump administration — which, along with more than a dozen other governments, has pledged its support for Guaidó — quickly condemned the action by Venezuela's chief prosecutor and vowed that any harm to the opposition leader would provoke "serious consequences." 

"We denounce the illegitimate former Venezuelan Attorney General's threats against President Juan Guaido. Let me reiterate - there will be serious consequences for those who attempt to subvert democracy and harm Guaido," national security adviser John Bolton tweeted Tuesday, echoing a similar warning he issued on Sunday. 

Since it recognized Guaidó as Venezuela's legitimate interim president, the Trump administration has escalated its efforts to isolate Maduro's authoritarian government. 

On Tuesday, Vice President Michael Pence met with Carlos Alfredo Vecchio, who the Trump administration has recognized as Venezuela's Chargé d'Affaires in Washington. After the meeting, Vecchio said Guaidó could be arrested by Venezuelan authorities. "This is a fight between democracy and dictatorship" he told reporters.