The Venezuelan government disputed Pompeo's account, saying it had instructed the U.S. diplomats to leave.
Also Thursday, the State Department confirmed it has revoked 340 USA visas from Venezuelans, including more than 100 former diplomats and their families. "They are fully dedicated to our mission of supporting the Venezuelan people's aspirations to live in a democracy and build a better future for their families".
The embassy closure is set to worsen already tattered relations with US President Donald Trump, who has not ruled out military intervention to oust President Nicolas Maduro as Washington monitors rapidly unfolding events in the oil-rich but crippled South American nation.
Pompeo addressed the Venezuelan people directly in a video tweet, saying the U.S.is eager to provide them desperately needed humanitarian assistance, including food and medicine.
Speaking on television and radio, Maduro said the "Command for the Defense of Basic Strategic Services" would be tasked with ensuring "security, operability and maintenance".
Protests are also planned in the capital of Caracas and other parts of Venezuela as US -backed Guaido seeks to ramp up pressure on Maduro, who says he is the target of a coup plot directed from Washington.
At a press conference on Thursday afternoon, State Department spokesman Robert Palladino revealed the government has revoked hundred of visas from "Maduro-aligned" Venezuelans over the last four days. The U.S. flag outside the embassy had been taken down.
The United States is one of about 50 countries that have thrown their support behind opposition leader Guaido, who has announced himself "interim president" after last year's disputed election. "The whole world knows who the saboteur is", he said.