Venezuela's opposition plans more marches Tuesday to press the military to let in US humanitarian aid, which President Nicolas Maduro says is the stepping stone to an invasion.
Opposition leader and self declared president Juan Guaido will lead a rally in eastern Caracas but demonstrations have been called all over the country.
They are to mark Youth Day but also to honour 40 people killed in anti-government rallies in January, many of them youths.
"We are going back to the streets to demand the entry of humanitarian aid that will save the lives of more than 300,000 Venezuelans," said Mr Guaido, who is speaker of the National Assembly.
Mr Maduro will counterattack by leading a march of young leftists protesting "imperialist intervention" in the center of Caracas, where the government says it will collect signatures of people who reject US President Donald Trump.
The tug of war between the government and opposition is centered on whether humanitarian aid will be allowed into the economically crippled country, which suffers shortages of food, medicine and other basics.
For five days, aid material including food and medicine has been piling up at collection centers in Colombia near the border with Venezuela.
A modern bridge linking two border towns has been blocked with two large containers and the tanker section of a big fuel truck.
The Venezuelan government distributed food and medicine on Monday.
Mr Guaido, recognised by some 50 countries, has offered amnesty to military personnel who dump Mr Maduro and told them that refusing to allow in badly needed aid is a crime against humanity.
The UN says some 2.3 million people have fled the country since 2015.
Mr Guaido says almost 100,000 Venezuelans have signed up as volunteers to help bring in aid and distribute it to those most in need.
Mr Maduro refuses to buckle, though, branding the aid convoys massing in Colombia a "political show" and a pretext for a US intervention.
Humanitarian aid has become a key factor in the power struggle between Mr Guaido, who last month proclaimed himself acting president, and Mr Maduro.
National Assembly president Guaido's envoys met with Brazilian officials in Brasilia and announced plans to establish a second aid storage center in the state of Roraima, on Venezuela's southeastern border.
Mr Guaido's ambassador to Brazil, Maria Teresa Belandria, said she had received assurances from Brazilian Foreign Minister Ernesto Araujo over the new aid center.
Lester Toledo, head of Guaido's aid distribution team, told reporters that the Roraima center would start receiving supplies next week.
But Defense Minister Vladimir Padrino announced that the armed forces were deploying a "reinforced presence all along the border."
On Sunday, dozens of doctors protested on the Venezuelan side of the border demanding the aid, which started arriving at the Colombian town of Cucuta on Thursday, be allowed into the country.
But the military has blockaded the border bridge linking the two countries.
The parliament speaker wants to oust Mr Maduro and set up a transitional government ahead of new elections. To do so, he needs the support of the armed forces.
Speaking to AFP last week, Guaido refused to rule out asking for foreign intervention.
The Venezuelan military meanwhile announced it had started conducting exercises, set to run until Friday, to "reinforce the country's defensive capacity."
Venezuela's financial accountability authority announced a probe into Mr Guaido's income, saying he had "allegedly... received money from international and national bodies without any justification."
Two weeks ago, the regime loyalist-dominated Supreme Court barred him from leaving the country and froze his assets.
Tuesday's march, in part to remember the estimated 40 people killed in clashes between protesters and the security services since January 21, aims to increase the pressure on Mr Maduro to step aside.
Mr Guaido warned that the military would be held responsible for the deaths of protesters.
The US is using sanctions as an attempt to starve Maduro's regime of its funding.
More than 40 percent of Venezuela's oil, which makes up 96 percent of its revenue, is sold to the US.
Pope Francis has said he would be prepared to mediate between the rival leaders but Mr Guaido has rejected negotiations with Mr Maduro, believing he would use them to buy time.
While keen on papal mediation, Mr Maduro was less impressed last week when a group of European and Latin American ministers called for new presidential elections. He accused them of bias.
Last week, he also rejected a call by European Union countries to hold elections, prompting them to recognise Mr Guaido.