“Many of them have been calling us saying: ‘What is going to happen? We want to stay with you, we want to recognize President Guaidó as the new president,’” Mr. Vecchio, 49, said in an interview in borrowed office space in downtown Washington.

The dueling diplomacy is critical in Venezuela’s political rivalry, as the envoys are responsible for maintaining support for their respective presidents from their host country’s leaders. Given Mr. Maduro’s reliance on political support from Moscow, for example, his ambassador is most likely firming ties with President Vladimir V. Putin and the Kremlin. Russia and Cuba are Mr. Maduro’s most important allies.

Mr. Vecchio is doing the same in Washington.

“Our interest is to just put in all the effort, all the pressure, to end the suppression of power, to end the dictatorship,” Mr. Vecchio said of his meetings over the last week with American officials.

“Of course, we will discuss how we can protect our assets right here,” he added.

So far, Mr. Guaidó has dispatched ambassadors to the United States, Canada, the Lima Group and eight Latin American countries. On Tuesday, Mr. Vecchio flew to Washington from his home in Miami, where he has been a political activist working with the Venezuelan opposition in exile, for a White House meeting with Vice President Mike Pence.

Also present was Julio Borges, the ambassador to the Lima Group, an organization of Western Hemisphere countries that have been trying to resolve the long-running instability in Venezuela.

“We were explaining to the vice president that this is a huge opportunity,” Mr. Vecchio said. “We need to take advantage of this. This is the moment to move forward with increasing the pressure.”

Mr. Vecchio told Mr. Pence and other American officials of the need to block Mr. Maduro’s government from obtaining Venezuela’s foreign assets and to instead turn them over to Mr. Guaidó. In the United States, that includes potentially billions from oil revenues sitting in bank accounts — the United States has imposed oil sanctions on Venezuela — and the embassy itself.