US Special Representative for Venezuela Elliott Abrams criticised the detention of executives from US refiner Citgo in Caracas and warned Russia over its support for Venezuelan President Nicolas Maduro.
The United States on Thursday warned Venezuela's rulers of consequences if opposition leader Juan Guaido is not allowed to return safely from a visit to Washington, where he enjoyed pledges of robust support.
In one sign that some saw as retaliation, authorities in Caracas threw into jail six oil executives with joint US and Venezuelan nationality, two months after allowing them to shift to house arrest.
Elliott Abrams, the US envoy leading the drive to oust leftist leader Nicolas Maduro, warned that the United States was "prepared" with unspecified actions if Guaido faces trouble.
"We hope that the regime makes the calculation, particularly after this trip, that the support for Guaido is strong and that the counter-reaction to any move against him would make it a mistake for the regime," Abrams told reporters.
"We're very concerned about it and we hope that he will return safely," he said.
Guaido, who is considered interim president by the United States and most other Western and Latin American nations, vowed to keep up his campaign.
"We are going to mobilise in the coming days in Venezuela," Guaido told reporters after meeting the head of the Organization of American States, Luis Almagro.
'Yes, there are risks.'
Guaido last week met Venezuelans in Miami and then appeared as a surprise guest on Tuesday at President Donald Trump's State of the Union address before Congress.
Guaido later met with Trump at the White House, which accorded him the same treatment it would any head of state.
Maduro's government harshly criticised both Trump and Guaido but in the past, it has allowed the opposition leader to move freely despite his efforts to topple the regime.
Guaido enjoyed applause across the political spectrum at the State of the Union address, despite a highly polarising speech by Trump, and met on Thursday with House Speaker Nancy Pelosi, the top Democrat in Congress.
Maduro presides over a crumbling economy, with millions having fled as they seek basic necessities, and his last election was widely criticised as fraudulent.
But a year-long US campaign to oust Maduro, including through sanctions to stop Venezuela's key export of oil, have failed to dislodge him.
Guaido's street protests have fizzled in size and Maduro still enjoys support from Russia, China and Cuba.
Abrams hinted that the United States would soon take action against Russia, amid reports Washington could target state oil giant Rosneft over its increasingly close relationship with Venezuela.
"Russia may soon find out that their continued support of Maduro will no longer be cost-free," Abrams said.
"You will see steps unfold in the coming weeks that demonstrate the seriousness of our intentions in Venezuela."
Executives back in jail
Hours after Guaido met Trump, Venezuelan authorities arrested six men with dual nationality who had been executives at Citgo, the US subsidiary of state-run Venezuelan oil firm PDVSA.
The executives – who two months earlier had been allowed to return to their homes – were taken to the detention centre of Venezuela's intelligence services, according to their families.
"They were rearrested, it seems, to have them respond to new accusations," said Gonzalo Himiob, director of Foro Penal, a Venezuelan non-governmental organisation that defends the rights of prisoners.
Alirio Rafael Zambrano, whose brothers Alirio Jose and Jose Luis Zambrano are among the Citgo executives, said they were taken "abruptly" from their home.
"We demand to know their whereabouts but more importantly their freedom!" he tweeted.
Abrams said that the timing of the arrests was "suspicious" and that the United States was deeply concerned about its six citizens' health.
"We condemn this cruel and indefensible action and demand that their long, unjust detention come to an end and that they be allowed to leave Venezuela," he said.
The executives were first arrested in November 2017 and accused of crimes including money laundering.
Their supporters scoff at the charges, saying the judiciary does the bidding of Maduro, whose regime has also been accused of corruption.