CARACAS/WASHINGTON (Reuters) – The White House warned traders on Wednesday not to deal in Venezuelan gold or oil following its imposition of stiff sanctions aimed at forcing socialist President Nicolas Maduro from power.

National security adviser John Bolton tweeted that traders should not deal in gold, oil or other commodities “being stolen” from the Venezuelan people, even as opponents of Maduro’s government worried that a Russian plane in Caracas was preparing to ship gold out of the country.

U.S. President Donald Trump spoke to Venezuela’s self-proclaimed interim president, Juan Guaido, by phone on Wednesday, reiterating support for his “fight to regain democracy.”

On one side of the tussle for control of Venezuela, an OPEC member that has the world’s largest oil reserves but is in dire financial straits, Guaido and Western backers led by the United States are insisting on an immediate transition and fresh elections.

On the other, Maduro, with backing from Russia, China and Turkey, says he will remain for his second six-year term despite accusations of fraud in his re-election last year and the economic meltdown.

Venezuela’s struggle to pay its debts even to allies Russia and China amid a sharp drop in oil output has been exacerbated by the new sanctions, which will make it very hard to sell oil to its main client, the United States.

In that context, the unusual arrival in Caracas of a Boeing 777 plane from Moscow on Monday led to speculation Maduro’s government was preparing to ship more gold reserves out of the country, following shipments last year of $900 million of gold to Turkey last year. Those shipments were part of a strategy to increase the Central Bank’s liquidity.

Venezuelan lawmaker Jose Guerra, a former Central Bank economist, told the National Assembly his understanding was that the plane would take some gold reserves to Russia when it leaves. The Central Bank did not respond to a request for comment.

Sources have told Reuters private military contractors who do secret missions for Moscow were in Venezuela.

Elliott Abrams, the U.S. envoy for Venezuela, said the United States was looking around the world for more assets of the Maduro government, including gold holdings and bank accounts

The Kremlin said this week it expected Venezuela to pay its debts. Russia, which like China has loaned and invested billions of dollars in OPEC member Venezuela, called on Guaido to drop his demand for a snap election and instead accept mediation.

But given the failure of previous rounds of dialogue between the government and opposition, including one led by the Vatican, opponents are suspicious, believing Maduro uses them to quell protests and buy time.

Guaido’s envoy to the United States, Carlos Vecchio, said the only dialogue they were interested in would be a negotiation for Maduro’s departure and new elections. Government officials insist the next presidential election will be in 2025.

FRESH PROTESTS

Responding to a call by Guaido, tens of thousands of protesters took to the streets in cities across Venezuela on Wednesday, some waving Venezuelan flags while drivers of cars and buses honked in support.

“I want this government to go, it has been a total humiliation for the country” said Lucy Cordoba, 51, a government worker in the poor hillside town of Petare at the edge of the capital, where she said trash had not been collected for a year and water was scarce.

Cordoba said her children were among the more than 3 million Venezuelans who have left the country in the past couple of years. One went to Peru, and another to Dominican Republic.

More than 40 people have died so far in and around the protests that began a week ago, the U.N. human rights office said. Hundreds have also been arrested, including children.

White House spokeswoman Sarah Sanders said Trump and Guaido agreed to maintain regular communication after Venezuelan authorities opened an investigation that could lead to Guaido’s arrest.

Oil prices rose nearly 3 percent on Wednesday, as investors remained concerned about supply disruptions because of Venezuela

Maduro, 56, says Guaido is staging a U.S.-directed coup against him. Facing the biggest challenge to his rule since replacing Hugo Chavez six years ago, Maduro told Moscow’s RIA news agency on Wednesday that Trump ordered “the government of Colombia and the Colombian mafia to kill me,” reprising an accusation of assassination plots that he has often made over the years.

Bogota and Washington have routinely denied that.

However, speculation about military action against him was fueled this week when Trump national security adviser John Bolton carried a notepad with the words “5,000 troops to Colombia”. U.S. Major General Mark Stammer, the commander of U.S. Army South, was in Colombia on Wednesday, U.S. embassy officials said.

In response to Guaido’s invitation to army officers to join his cause in return for an amnesty, Maduro has made daily visits to troops, whose pledges of allegiance are televised. He is not expected to stand down while he has the backing of senior military officers.

“Do you want to be a coward,” he yelled in a call and response session with hundreds of soldiers on Wednesday.

“No, president,” they shouted back.