The United States on Friday intensified its push to drive Venezuelan President Nicolas Maduro from power, as US diplomats left the embassy in Caracas and Russia vowed to back its South American ally.

US Secretary of State Mike Pompeo on Saturday will urge the members of the United Nations Security Council to recognise opposition leader Juan Guaido as Venezuela's legitimate head of state.

Washington requested the meeting of the 15-member council after a string of countries threw their weight behind Guaido, who heads Venezuela's Congress, and urged Maduro to step down.

Russia opposes the request and has accused Washington of backing a coup attempt, placing Venezuela at the heart of a growing geopolitical duel. Moscow will insist on compliance with international law, Russia's RIA news agency cited Foreign Minister Sergei Lavrov as saying on Friday.

Maduro said he welcomed a debate over Venezuela's situation and thanked Pompeo for making the UN request, in a jocular response during a news conference on Friday.

"I was about to say to the foreign minister 'ask for a Security Council debate,' (but) Mike Pompeo got ahead of me," Maduro said. "Thanks, Mike ... We're going to tell the truth about the articles of the constitution, about the coup."

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Earlier, American diplomats left the US embassy in Caracas in a convoy of vehicles with a police escort en route to the airport, according to Reuters news agency.

In a fiery speech on Wednesday, Maduro had broken off diplomatic relations with Washington and ordered the US personnel out within 72 hours.

The State Department on Thursday told some US government workers to leave Venezuela and said its citizens in the country should consider leaving. It did not immediately respond to a request for comment on the movement of embassy personnel on Friday.

UN human rights boss Michelle Bachelet called on Friday for an investigation into the alleged excessive use of force by Venezuelan security forces against protesters, adding that she was "extremely concerned" that the situation could rapidly spiral out of control.

'No fake dialogue'

Guaido, who has galvanised Venezuela's opposition, proclaimed himself interim president on Wednesday during a march of hundreds of thousands in Caracas. He is considering making a request for funds from international institutions, including the International Monetary Fund, two people familiar with the talks said on Friday.

However, he still has no control over the Venezuelan state and the military, which have so far remained loyal to Maduro.

Guaido has promised future amnesties to military members if they disavow Maduro.

On Friday, Guaido repeated his offer to the armed forces around Venezuela, asking soldiers "to put themselves on the side of the constitution". He also called for mass protests next week.

Most Latin American nations have joined the US in supporting Guaido's claim on the presidency, although Mexico's new leftist government has said it would not take sides. Mexican President Andres Manuel Lopez Obrador said on Friday his administration would be willing to mediate.

Guaido said he would reject any negotiations that did not include Maduro's exit, setting up a transition government and free elections to pick a new president.

"No one wants fake dialogue ... the only thing we want to negotiate is the end of the usurpation," he told a crowd clustered in a plaza in Caracas's Chacao district, an opposition stronghold.

For his part, Maduro said he would be willing to engage in talks with the opposition to avoid violence.

"I'm committed to a national dialogue. Today, tomorrow and always, I'm committed and ready to go wherever I have to. Personally, if I have to meet with this young man ... I'll go," the leader said.

Analysts believe Maduro's strategy may be focussed on gaining time.

"In the past, when Maduro's government has faced [similar situations] he has always opted for a strategy in which he calls for national and international dialogue," said Carlos Eduardo Pina, a Venezuelan political scientist.

"He is aiming to gain time. He has done this in the past and he has succeeded," Pina added. "[Maduro] has managed to dismantle the opposition forces, their leaders, and their supporters, making them seem as incapable of reaching their own political agenda."

US seeks to cut off funds

To ratchet up pressure on Maduro, who began a second term on January 10 following an election last year widely considered to be fraudulent, the US is seeking to cut off funds for his government, officials said on Thursday.

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Guaido is also readying a new board to run state-run oil firm PDVSA's US unit Citgo Petroleum, people familiar with the discussions said.

Maduro warned off any attempt to take control of Citgo, the country's primary offshore asset.

"It is the property of the Venezuelan people, and we will defend it," he said.

The Maduro-appointed board of Citgo is preparing a legal strategy to defend itself, sources close to the talks said.

Oil prices edged higher on Friday as the political turmoil threatened to tighten the global supply of crude.

Washington has signalled that it could impose new sanctions on OPEC member Venezuela's vital oil sector.

"The oil situation has been an ethical moral dilemma for us," said US Senator Richard Durbin, the second-ranking Democrat in the Senate.

"Cutting off all trade in oil would be the last step. It would make it even worse for the average person."