(CNN) The man who proclaimed himself acting Venezuelan president -- in open rebellion to President Nicolas Maduro's regime -- called on the nation's military Friday to work with him.

"Come to the side of the Venezuelan people," Juan Guaido said in a message aimed at the armed forces.

His appeal was made during a speech to a crowd at a public square in Caracas a day after the head of the armed forces announced continued support for the embattled President.

Maduro, meanwhile, said Friday that he is willing to sit down with the opposition to resolve the political crisis.

"We believe that it's only possible through dialogue and diplomacy to find solutions to conflicts," he told reporters at the presidential palace. "Not through violence or foreign interventions or coup attempts or war."

He challenged the military on Friday to allow foreign aid into the economically strapped country if and when it comes.

At least 20 people have died in protest-related violence

US Secretary of State Mike Pompeo had said earlier this week that the US -- which now recognizes Guaido as president -- will offer $20 million to address food and medicine shortages "as soon as logistically possible."

"Are you or are you not" going to allow the aid to come in? Guaido asked the military rhetorically.

The back and forth came as a UN human rights official said at least 20 people had died in protest-related violence this week, sparking her concern that the situation there "may rapidly spiral out of control."

The 20 people allegedly were shot to death by security forces or members of pro-government armed groups during demonstrations Tuesday and Wednesday, UN human rights High Commissioner Michelle Bachelet said Friday, citing "credible local sources."

The Observatorio Venezolano de Conflictividad, a Venezuelan NGO, reported Friday evening that 29 people have been killed in nationwide protests. The group said the count started at midnight on Wednesday.

CNN could not independently confirm either count.

Pompeo on Friday told reporters that he had appointed Elliot Abrams, the former deputy national security adviser for President George W. Bush, to lead efforts in resolving the crisis. He also said "all appropriate measures" were being taken to ensure the safety of US diplomats in Venezuela.

Guaido, in his first public appearance since his dramatic challenge to the regime, said a massive rally planned for next week is intended to signal that his anti-Maduro movement is gaining momentum.

"The people who think that we are going to fizzle, I think they are not going to be happy," he said Friday. "There are people here in the streets for a long time."

At Maduro's presidential palace news conference, days after announcing that he was cutting diplomatic ties with the US, the President seemed to soften his stand. He said he had broken "political and diplomatic relations" with President Donald Trump but maintains other relations with US.

But a US State Department spokesperson said Friday, "The United States does not recognize the Maduro regime as the government of Venezuela. Accordingly, the United States does not consider former president Nicolas Maduro to have the legal authority to break diplomatic relations with the United States, declare our diplomats personae non grata or close Venezuelan diplomatic missions in the United States."

In a statement Friday, the US Treasury Department said it plans to use economic and diplomatic tools to ensure any commercial transactions with the Venezuelan government are "consistent" with the US-recognized government of Venezuela led by Guaidó.

The crisis has taken a country on a prolonged political and economic collapse to a new low point.

More than 350 demonstrators have reportedly been detained during the scores of protests this week, Bachelet's office said.

"I am extremely concerned that the situation in Venezuela may rapidly spiral out of control with catastrophic consequences," Bachelet said.

Venezuelan President Nicolas Maduro spoke at Venezuela's Supreme Court on Thursday.

The power struggle has sparked a diplomatic row as well, with the United States and at least a dozen other countries saying they'll recognize Guaido, while Russia, China and others back Maduro.

Maduro, who accuses the United States of meddling, said Thursday he was closing Venezuela's embassy and all its consulates in the United States, and has given US diplomats until this weekend to leave his country.

"I believe there's no doubt that [US President] Donald Trump wants to impose a de facto government, unconstitutional government, a coup against the people and democracy in Venezuela," Maduro said Thursday in a lengthy speech that aired live on state broadcaster VTV. "There's no doubt that is Donald Trump with his craziness of believing he's the world's police."

Guaido wants diplomats to stay in US

Speaking at Venezuela's Supreme Court on Thursday, Maduro said Venezuela's diplomats and consulate personnel in the US will return to the Latin America country by Saturday.

Maduro reiterated his decision to cut diplomatic ties with the US and continuously slammed President Donald Trump, among other top US officials.

All non-emergency US employees were ordered to leave Venezuela on Thursday, according to a security alert. Pompeo had earlier brushed off Maduro's order that US diplomats leave the country, saying the US doesn't recognize his power to do so.

The US Embassy in Caracas opened Thursday but all visa appointments were canceled.

Late Thursday night, Guaido called on Venezuelan diplomats to stay in the US.

Guaido also said he would consider amnesty for Maduro and his allies if they don't hamper Guaido's ascension to temporary power. He has called for elections.

A fire burns during a protest Wednesday in Caracas against the government of Nicolas Maduro.

Venezuela military loyal to Maduro

Military commanders and the country's defense minister expressed allegiance to Maduro on Thursday.

In military dress uniform and flanked by members of the military's high command, Defense Minister Vladimir Padrino said Maduro was the country's legitimate leader -- and that Washington and other regional powers were trying to "knock out progressive governments that make them uncomfortable."

Venezuelan Defense Minister Vladimir Padrino, flanked by senior members of the country's military, speaks in support of President Nicolas Maduro on Thursday.

"We will not bend to foreign intervention or a government not elected by the people," Padrino said in an address aired by state broadcaster VTV.

Moments before Padrino spoke, VTV aired messages of support from Venezuela's eight regional commanders from their military outposts throughout the country.

US calls for Security Council meeting

Pompeo urged all members of the regional Organization of American States to support Guaido, saying Maduro's regime is "now defunct" and illegitimate.

People cheer as they listen to Venezuela's National Assembly head Juan Guaido during a mass opposition rally against leader Nicolas Maduro.

ture, is ready to give Venezuela $20 million in aid to help with food and medicine shortages, to be distributed "as soon as logistically possible."

Trump vowed in a statement Wednesday to use "the full weight of United States economic and diplomatic power to press for the restoration of Venezuelan democracy."

Trump said he is prepared to take a range of actions against Venezuela, including possible oil sanctions, two sources familiar with White House deliberations said.

Countries divided over leadership crisis

While many world leaders quickly expressed their support for Guaido this week, many others stood behind Maduro.

Describing Maduro's regime as illegitimate, several countries, including the United States, Argentina, Brazil, Canada, Chile, Colombia, Ecuador, Paraguay and Peru, recognized Guaido as president.

These are the countries that support Guaido Argentina

Brazil

Canada

Chile

Colombia

Costa Rica

Ecuador

Guatemala

Honduras

Panama

Paraguay

Peru

United Kingdom

United States

British Foreign Secretary Jeremy Hunt said the UK believes "Juan Guaido is the right person to take Venezuela forward."

European Council President Donald Tusk expressed support for him and called on other European countries to join him.

These are among the countries that support Maduro Bolivia

China

Cuba

Nicaragua

Russia

Syria

Turkey

Russia, China, Cuba and Turkey are among the nations backing Maduro -- and Russia in particular is criticizing the United States for undermining him.

Washington's interference in Venezuela could lead to "lawlessness and bloodshed," the Russian Foreign Ministry said in a statement.

A few other countries like Mexico have said they prefer to stay on the sidelines. Mexico's Foreign Minister Marcelo Ebrard said Thursday the country will follow its policy of nonintervention.

UN Secretary-General Antonio Guterres has called for dialogue.

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This is not the first time that the US and many of Venezuela's neighbors have refused to recognize Maduro's presidency. His election in May and the country's deep economic crisis was a flashpoint for many of them.

The election was boycotted by opposition groups and largely discredited by opponents, with hundreds of complaints of election violations and a low turnout.

This story has been updated to correct the spelling of Juan Guaido's last name.