Washington (CNN) The US State Department on Thursday evening ordered all non-emergency government employees to depart Venezuela amid an ongoing diplomatic crisis in the country.

They also warned in a security alert that US citizens "residing or traveling in Venezuela should strongly consider departing" while flights remain available.

"The U.S. government has limited ability to provide emergency services to U.S. citizens in Venezuela," the alert said. "If choosing to stay, ensure you have adequate supplies to shelter in place."

The announcement comes just hours after embattled Venezuelan President Nicolas Maduro said he is closing the Venezuelan Embassy in the United States and all Consulates, as well as pulling out all diplomatic staff from the country.

"I have decided to return all our diplomatic and consular staff from our country that is abroad and close our embassy and all of our consulates in the United States," Maduro said, during a speech at the Venezuela Supreme Court in Caracas that was aired live on state broadcaster VTV.

Maduro, who appeared wearing the presidential sash, said Venezuelan diplomatic staff was expected back in Caracas by Saturday, adding that they would hold "a festive welcoming act" for the returning staff. He reiterated his demand for US diplomatic personnel to leave Venezuela.

"They have until Sunday, that is their 72-hour deadline to leave Venezuela. To get out of Venezuela," Maduro said. "I'm telling the State Department, in a sensible and rational way and based on international law, they must follow the order that has been issued by the Venezuelan government."

Administration officials had earlier dismissed Maduro's Wednesday announcement that he was cutting ties with the US and ordering American diplomats to leave within 72 hours as "meaningless."

Regarding the US Embassy is Caracas, national security advisor John Bolton said on Thursday morning that personnel had "been invited to stay by the legitimate government."

A senior State Department official told CNN Thursday morning that "there are no plans to close the embassy."

"We are closely monitoring the situation. Safety and security are, as always, a top priority," the official said. A State Department spokesperson reiterated that they were monitoring the situation "in real time," noting that they were "prepared to do the things we need to do to make sure we keep our people safe.""

Prior to the announcement of the ordered departure, Reps. Eliot Engel (D-New York ) and Michael McCaul (R-Texas), the chairman and ranking member of the House Foreign Affairs Commitee, wrote a letter to Secretary of State Mike Pompeo Thursday to request "immediate briefings and written materials on all efforts to keep U.S. government employees and their families in Caracas safe and contingency plans for these individuals to exit the country if needed."

"Regardless of the Administration's policy toward Venezuela, we all agree on the need to keep our diplomats in Caracas safe from harm by making staffing decisions for the U.S. Embassy based on the well-being of these individuals and their families," the congressmen wrote.

The Secretary of State and the State Department have called on Venezuelan military and security forces to protect Guaido and the citizens of Venezuela, as well as US and other foreign citizens in the country.

Earlier Thursday, Venezuela's Armed Forces pledged allegiance to Maduro through written and video messages which aired on state broadcaster VTV.

Defense Minister Vladimir Padrino spoke Thursday from the Defense Ministry Headquarters in Caracas, saying the Armed Forces were standing by "the legitimate president" of Venezuela and accusing "the far right" of installing a "parallel de facto government" and leading a "coup against Venezuela's democracy."

Lights out at the Venezuelan Embassy

By Thursday afternoon, lights were off at the embassy in Washington, DC and a sign was posted on the door noting that there would be no consular services there "until further notice."

The US State Department denounced the move to close the Venezuelan missions in the US.

"The United States expects the same treatment we accord all diplomats within our borders," a State Department spokesperson said. "We urge the good people of Venezuela, from those working to keep the lights on to those charged with protecting people, to stand with their fellow Venezuelans, the struggle for democracy, and do the right thing."

The spokesperson also said the US is ready to support Guaido as he "establishes a transitional government and carries out his duties as interim President, including determining the status of diplomatic representatives in the United States and other countries."

'Very, very sad situation'

On Thursday afternoon, President Donald Trump called Venezuela "a very, very sad situation."

"We have our eye very closely on Venezuela. Very closely," he said.

The US President's decision on Wednesday to recognize Guaido, the Venezuelan opposition leader, as the country's interim president, a move that has set the stage for dramatic escalation in the coming days, as forces within and outside Venezuela wrestle to determine its future.

Thirty-five-year-old Guaido swore himself into office and declared that Maduro had been deposed -- though analysts say it's not clear the former bodyguard's fall is anywhere near imminent or that Trump's power play will pay off.

The European Union and several Latin American countries are also supporting Guaido.

China, Russia and Turkey have voiced support for Maduro.

Maduro on Thursday also accused Trump of wanting "to install a de facto unconstitutional government" in Venezuela.

"There is no doubt that it is Donald Trump, with his craziness, who thinks he can police the world: who thinks he has more power than anyone in Latin America and the Caribbean," he said.

Maduro's remarks come hours after Pompeo urged all members of the Organization of American States to support the interim presidency of Juan Guaido in Venezuela, referring to Maduro's regime as "now defunct" and "illegitimate."

"We call on the OAS and all its member states to act on basic, decent democratic principles and the incontrovertible facts on the ground," Pompeo said.

"His regime is morally bankrupt, it's economically incompetent and it is profoundly corrupt," he added about Maduro. "It is undemocratic to the core."

As Pompeo spoke at the OAS, White House national security adviser John Bolton told reporters on the North Lawn that Trump's assertion Wednesday that all options were on the table regarding the situation in Venezuela "speaks for itself."

"All options (are) on the table," Trump told reporters Wednesday when asked if he might use military force to ensure the outcome he wants in Venezuela. "All options, always, all options are on the table."

Bolton also said Thursday that the administration is focusing on disconnecting the Maduro regime from its sources of revenue.

"We think consistent with our recognition of Juan Guaido as the constitutional interim president of Venezuela that those revenues should go to the legitimate government. It's very complicated. We're looking at a lot of different things we have to do but that's in progress," Bolton said.