Caracas, Venezuela (CNN) The political momentum of Venezuela's opposition swelled Saturday with street protests in Caracas, while President Nicolas Maduro stood defiant in the face of domestic and international pressure against his rule.

Maduro underscored the need for a strong military and invited his countrymen to "join to start strengthening our defense."

"We are preparing to defend the sacred motherland," he told supporters, "in case they one day dare to mess with our beloved Venezuela."

But Maduro's opposition grew further Saturday, with massive demonstrations and the reported defections of a top military official and the first Venezuelan ambassador.

Jonathan Velasco, the Venezuelan ambassador to Iraq, declared his support for the self-declared interim president Juan Guaido. In a recorded statement circulating on social media, Velasco praised Guaido as being on the "right side of history, the people and the Constitution."

CNN cannot independently verify the origin or authenticity of the video.

Opposition leader Juan Guaido's 'very clear message'

Guaido urged people inside and outside Venezuela to show their support in peaceful protests.

Tens of thousands heeded Guaido's call as demonstrators hit Caracas' streets in support of early elections.

Maduro has been under fire by world leaders for undermining democracy in his country, which has been plagued by food and medicine shortages and other economic turmoil.

Guaido, the leader of the opposition-controlled National Assembly, declared himself acting president last week, invoking a constitutional rule in a rare challenge to Maduro's claim to the presidency.

"In all the states of Venezuela and in every city in the world, we are going to send a very clear message. We are going to give a show of strength, in a peaceful and organized way," Guaido said Saturday on Twitter.

"Today Feb 2nd, we are going to meet again in the street to show our gratitude to the support that the European Parliament has given us, to continue insisting on the entry of humanitarian aid and to continue our path towards freedom."

Guaido also told a rally Saturday that much-needed international aid destined for Venezuela will be stockpiled in three places -- in Cucuta, Colombia, in Brazil and on a Caribbean island.

Carlos Vecchio, the opposition representative to Washington, told CNN this week that "this is an international effort. We are fully aware that the people of Venezuela are suffering because of lack of food and medicine. And Maduro hasn't allowed to get this food, get ... medicine ... in."

Maduro supporters mark the 20th anniversary of Hugo Chavez's rise to power on Saturday in Caracas.

Pro-Maduro marches also were underway Saturday in Venezuela, commemorating the 20th anniversary of the inauguration of the first government of Maduro's mentor and predecessor, the late President Hugo Chavez

Maduro assured his supporters that "there will not be a dictatorship in Venezuela" and reiterated his initiative for a dialogue to heal divisions.

He said the pro-government Constitutional Assembly is studying the possibility of early parliamentary elections "this very year."

"I am in agreement with rectifying the legislative power of the nation and going forward with free elections in the nation with guarantees, and for the people to decide on a new National Assembly," he told a Caracas rally.

The opposition National Assembly took office in 2016, and its mandate runs through 2021.

But Maduro has refused an opposition call for early presidential elections, and he was firm Saturday about his role as the country's leader: "I am the president of the Bolivarian republic of Venezuela, and I owe myself to everyone, not just some of them, I owe myself to all of Venezuela. Sovereign president, acting president, the workers' president, the president of the people, President Maduro, Chavista President!"

What will the military do?

With pro-government and opposition protesters turning out in the streets, the military may play a key role in what happens next in Venezuela.

In an on-camera statement published online Saturday, a man identifying himself as Gen. Esteban Yanez Rodriguez of the Venezuelan air force's high command said he has defected from Maduro's military and declared his support for Guaido.

Venezuela's air force website lists Yanez as the head of air force strategic planning. An accompanying photo appears to show the same man as in the defection video.

The video has been edited, and CNN cannot independently authenticate it. It's not clear when or where it was filmed.

The man in the video said he no longer recognizes the dictatorial authority of Maduro and claimed that "90% of the armed forces" do not support Maduro but stand with the people of Venezuela.

"To continue ordering the armed forces to repress the people is to have more dying of hunger and illness ... ," he said.

He appealed to his "brothers in arms" not to turn their backs on the people of Venezuela, saying all have suffered enough.

The video announcement comes a week after Venezuela's military attaché in Washington, Col. Jose Luis Silva Silva, told CNN that he's breaking with Maduro and supporting Guaido.

With some 1,000 or so generals reportedly in Venezuela's military , there have not been many other signs of mass desertion in the upper ranks so far, according to CNN senior international correspondent Nick Paton Walsh, who was recently inside Venezuela.

But the timing of the latest defection is most potent since it comes amid large-scale protests Saturday in Venezuela and other cities around the world, Walsh said.

Venezuela's air force command reacted to the defection on Twitter, calling Yanez a "traitor."

"Worthless is the man of war who betrays the loyalty and fidelity swearing of the land of Bolivar and the legacy of Comandante Hugo Chavez, and kneels before the imperialist pretensions," the air force command tweet said.

At a pro-government rally in Caracas Saturday, Maduro called on the militia to join the Venezuelan army.

"I call the militia men and women to sign up for your military service," Maduro said.

He also encouraged more people, "especially the youth," to sign up for the military.

Maduro noted forthcoming military exercises in February, calling them "the most important and greatest military exercises" in Venezuela's history as a republic.

"We are preparing to defend the sacred motherland in case they one day dare to mess with our beloved Venezuela," Maduro said.

More than a dozen countries, including the United States, have recognized Guaido. Mexico and Uruguay called for an international conference of neutral countries to facilitate talks next week between Maduro and the opposition.

Maduro began a six-year presidential term last month. He has said last year's elections were fair, but international observers have questioned their legitimacy.

Guaido has promised a transitional government and free elections to end the rule of the socialist Maduro regime, which has overseen the once-wealthy oil nation's descent into economic collapse and a humanitarian crisis.

Besides the United States, several European and Latin American countries are supporting Guaido, and the European Parliament recognized him as Venezuela's "legitimate interim President."

China, Russia and Turkey are among the countries that have voiced support for Maduro.