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The U.S. State Department ordered all nonemergency government staff out of Venezuela on Thursday and advised other Americans in the country to leave.

The State Department security alert came a day after Venezuelan President Nicolás Maduro ordered the U.S. to close its embassy in Caracas and get all of its diplomatic employees out of the country.

Maduro gave them 72 hours to leave after President Donald Trump announced Wednesday that the U.S. no longer recognizes the Maduro government. Secretary of State Mike Pompeo shot back Wednesday that the U.S. didn't recognize Maduro as having "the legal authority to break diplomatic relations."

The U.S. is keeping its embassy in Venezuela open, according to the State Department announcement. "This is a reduction in staff but not a closing of the embassy," the alert says.

U.S. citizens traveling or living in the country were also advised to "strongly consider departing," in the announcement. It advised Americans in Venezuela to consider leaving "while commercial flights are available," adding that those who stay should "ensure you have adequate supplies to shelter in place."

Prior to the announcement Thursday, a former career diplomat said the Trump administration should remove personnel without delay to reduce risk to Americans stationed there.

"What we really need to start telling citizens is: 'This is the time to get out. This is the time to prepare,'” said Brett Bruen, who served in Venezuela and whose most recent government posting was as director of global engagement during the Obama administration.

Bruen recalled that in 2003 the U.S. withdrew most of its staff from the embassy in Liberia when rebels threatened the capital city of Monrovia.

President of the Venezuelan National Assembly Juan Guaido participates in an Open Cabildo (open forum), in Caracas, Venezuela on January 19, 2019. Miguel Gutierrez / EPA

“It’s a lot easier to extract two or three people, than it is to extract two or three thousand,” said Bruen.

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The U.S. has long been at odds with Maduro and his predecessor, Hugo Chavez, the socialist leader who was elected in 1998 and used revenues from the oil boom to spend heavily on social programs. He died in 2013 just before oil prices dropped sharply and Maduro took over.

The simmering conflict erupted into a full-blown crisis on Wednesday when Venezuelan opposition leader Juan Guaido declared himself interim president and the U.S. and several other countries threw their support behind him.

Sen. Marco Rubio, R-Fla., said in an interview Thursday with NBC’s Andrea Mitchell that the goal is for a peaceful transition of power in Venezuela. But, he said, “All options are on the table because the United States always retains the option of protecting its national security.”

Longtime Venezuela watcher Brian Fonseca, a professor at Florida International University and an expert on that country’s military, said he believes Maduro’s order for U.S. personnel to leave “was probably a big miscalculation.”

“I don’t think he’s going to arrest them, take them hostage, march them to the airport,” said Fonseca. “I think they will stop short of any provocation that will justify Rubio asking Trump to send in the Marines.”

Fonseca said ultimately it will be the Venezuelan military that decides whether Maduro stays or goes.

“The military holds the key to any transition,” he said. “It is easily the most respected institution in Venezuela.”

Security forces look on while clashing with opposition supporters participating in a rally against Venezuelan President Nicolas Maduro's government and to commemorate the 61st anniversary of the end of the dictatorship of Marcos Perez Jimenez in Tachira, Venezuela on January 23, 2019. Carlos Eduardo Ramirez / Reuters

Prior to the State Department announcement Thursday, a prominent Maduro supporter appeared to threaten to cut electricity at the U.S. embassy.

“They say they don’t recognize Nicolas,” said Diosdado Cabello, who heads Venezuela’s Constituent Assembly. “OK. Maybe the electricity will go out in that neighborhood, or the gas won’t arrive. If there are no diplomatic relations, no problem.”

Geoff Ramsey, a Venezuela expert for the WOLA advocacy organization, said the Venezuelan military still has Maduro’s back.

“We have not seen any evidence of any kind of meaningful break in the military or within Maduro’s inner circle,” he said.

Russia, an ally of Maduro, warned the U.S. on Thursday not to intervene militarily in Venezuela.

Fonseca said he doesn't believe Moscow would take action.

"The Russians talk a lot but they don’t have any skin in the game," Fonseca said. “I think the Russians want to keep Venezuela a mess because it keeps U.S. foreign policymakers occupied. Venezuela is not that important to them. This is not Ukraine or Georgia.”

Asked how the Venezuelan crisis might end, Fonseca said time is a factor.

"The longer it goes on the more the outcome favors Maduro and not the opposition," he said. "I think yesterday was an attempt by the U.S. to deliver a first-round knockout."

Sesin reported from Miami, Siemaszko from New York.