The embattled Nicolas Maduro regime halted plans to ship 20 tons of Venezuelan gold overseas as a growing international push to ring-fence the country’s dwindling hard assets unnerved those handling the transaction, according to a person with direct knowledge of the matter.

The gold bars had been weighed and separated for shipment, but will not be sent out from the central bank’s vaults in Caracas. The person didn’t know where the gold was supposed to go or the exact nature of the planned transaction, but the fate of the bars had become a cause of great concern both in Venezuela and abroad. Valued at about US$850 million, they are an important source of wealth in a country that has plunged into extreme poverty under Maduro’s leadership.

On Thursday, Marco Rubio, the Florida senator who has helped spearhead the U.S.’s hard-line stance toward the Maduro regime, fired off a tweet calling out the United Arab Emirates’ Noor Capital as the financial firm orchestrating the gold transaction with Venezuelan authorities. Rubio went on to warn the firm that both it and any airline it hires to take the gold away will be subject to U.S. Treasury sanctions.

Rubio’s warning came a day after National Security Adviser John Bolton sent a similar message to the investing community. “My advice to bankers, brokers, traders, facilitators, and other businesses: don’t deal in gold, oil, or other Venezuelan commodities being stolen from the Venezuelan people by the Maduro mafia,’’ Bolton said in a tweet.

Twenty tons is a lot of gold bars -- almost 1,600 of them. Together, they represent about 10 percent of all the Venezuelan central bank’s foreign reserves. Those assets form a key part of the fierce battle for control of Venezuela’s finances between Maduro and Juan Guaido, the National Assembly leader who is trying to install a transitional government with the support of the U.S. and other countries across the region.

In interviews and press conferences, Guaido has stressed again and again his team’s push to safeguard Venezuela’s assets so that they can be used to fund the flow of humanitarian aid. He has scored key victories in recent days on this front. The Trump administration imposed fresh sanctions on the national oil company PDVSA, effectively blocking Maduro from exporting crude to the U.S., and granted Guaido control of Venezuelan assets at the Federal Reserve Bank of New York.

And last week, the Bank of England denied Maduro officials’ request to withdraw US$1.2 billion of gold stored there after top U.S. officials, including Bolton and Secretary of State Michael Pompeo, lobbied their U.K. counterparts to cut off the regime from its overseas holdings.

“The English stole the gold in the Bank of England,” Diosdado Cabello, the powerful No. 2 in Maduro’s socialist party, said in a speech broadcast on state television this week. “The imperialist bosses should know that we will never give up.”