Venezuelan opposition leader Juan Guaido was on Sunday set to announce a date for the arrival of humanitarian aid to the crisis-wracked country -- a path President Nicolas Maduro believes will lead to a US-led military intervention.

During the protest, Guaido announced the installation of collection centers for medicine and food in neighboring Colombia and Brazil. The United States later said it would transport aid to Venezuela in response to a request by Guaido.

The 35-year-old received a boost before the demonstration had even started when an air force general became the highest ranking officer to abandon Maduro and recognize Guaido as the country's true leader.

US National Security Advisor John Bolton responded to that in a tweet calling on "all military members to follow General (Francisco) Yanez's lead." The United States recognized Guaido as Venezuela's interim president on January 23 while four major European nations -- Britain, France, Germany and Spain -- have said they will do likewise unless Maduro calls presidential elections by midnight on Sunday.

Speaking at a pro-regime demonstration marking 20 years since his predecessor Hugo Chavez came to power, Maduro ignored those demands and instead reiterated his call to bring forward legislative elections slated for the end of 2020 to this year.

"They (the opposition) want to bring forward elections, let's have elections," he said.

Maduro, making his first public appearance since a military parade in August when he claimed to have been targeted in an attempted assassination, accused Guaido of being a US "puppet" in a coup d'etat attempt.

The National Assembly is the only one of Venezuela's five government branches controlled by the opposition.

Guaido had earlier urged the armed forces to allow humanitarian aid from abroad into the country.

"You, soldier... have the decision in your hands" to allow it in or not, said Guaido. Under Maduro's stewardship, oil-dependent Venezuela has lurched into an economic crisis that has left the country suffering from hyperinflation and shortages of food and medicine.

But he refuses to let aid into Venezuela, claiming it would precede a US-led military intervention.

Guaido also called for a new demonstration on February 12, and another protest to push for the entry of humanitarian aid.

Speaking at the European Union's headquarters in the east of the capital, he said this month "should be decisive." The rival Caracas rallies, separated by 10 kilometers (six miles), attracted huge crowds.

Carlos Morales, a 62-year-old who voted for Chavez in 1998 but now says socialism only brings "misery," attended a pro-Guaido rally with his wife. "This is the leader that all Venezuelans hoped for, a new leader, young, who is not contaminated," he added.

At the pro-Maduro demonstration, Virginia Rondon, 69, hummed songs that glorified Chavez, and reminisced about his socialist revolution, saying: "I never experienced anything more beautiful in all my years."

Others denounced the specter of US intervention and called on the United Nations to halt "Trump's war." Early on Saturday, General Yanez said in a social media video that he disavowed Maduro's "dictatorial" authority and recognized Guaido as the acting president.

The air force high command strategic planning director said "90 percent of the armed forces don't support the dictator." His defection is "a hard blow" to Maduro, said Rocio San Miguel, an expert on the Venezuelan military.

Later, in another video, retired Major General Jorge Oropeza, former air force general commander, also said he recognized Guaido as acting president.

Oropeza and Yanez were also joined by Jonathan Velasco, Venezuela's ambassador in Iraq.

The military and security forces have so far been Maduro's main pillar of support, but there have been signs of unrest in the ranks. On January 21, a group of 27 soldiers rose up against Maduro in Caracas, although that was quickly suppressed.

It helped spark a week of protests in which 40 people were killed in clashes with security forces, with hundreds more arrested.

The challenge to Maduro is his most serious yet, with the United States leading the campaign to drive him from office.

Guaido moved to expand his international support by reassuring China -- Venezuela's main creditor and a long-time ally of the socialist regime -- that he would honor bilateral agreements if successful in ousting Maduro.

China, like Russia, has denounced outside interference in Venezuela. Guaido told the South China Morning Post he would not disrupt the relationship with China despite his close ties to Washington.

"China's support will be very important in boosting our country's economy and future development," he said in an email interview.

China's foreign ministry spokesman Geng Shuang said cooperation between the countries would continue "no matter how the situation changes" in Venezuela.

(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)