Mr. Guaidó said the temporary government “must be broad and include all the political and social sectors necessary to confront this grave emergency that is coming to us.” However, he maintained that it could not include Mr. Maduro or those of his supporters who, like the embattled president, were charged with drug trafficking last week by the United States.

With a power-sharing government, Mr. Guaidó said in a statement, international organizations may consider loaning Venezuela at least $1.2 billion to counter the pandemic, which he said could force people to “choose between dying from the virus or from hunger.”

In his speech on Monday night, Mr. Maduro appeared to threaten “all the plotters” to his rule with a brief reference to “Operation Knock-Knock” — raids by government security forces, beginning in 2017, that yanked political opponents from their houses at night. Several of Mr. Guaidó’s top officials, opposition lawmakers and a journalist have been detained in the past two weeks in the latest wave of the roundups.

The United States’ plan is based on proposals that were discussed last year between the sitting government and the opposition before negotiations broke down over whether Mr. Maduro would leave power. At the time, Mr. Maduro’s negotiators had also insisted that the United States lift sanctions against the government that have sought to cut off its oil exports and estrange it from the rest of the world.

Mr. Abrams said some sanctions against specific people in Mr. Maduro’s administration could be lifted as their roles in a power-sharing government shifted. But he said the most bruising financial penalties — including those that freeze the sitting administration’s assets and properties — would remain until Mr. Maduro steps down and the temporary government is empowered.