Many Venezuelans have no access to food or medical supplies. Acting President Nicolas Maduro denies that any humanitarian crisis is taking place and has called on the military to block any aid from entering the country.
Acting President Nicolas Maduro ordered the closure of Venezuela's border with Brazil on Thursday, saying earlier in the day that the border would remain "completely and absolutely" shut "until further notice.".
Maduro said he was also considering closing the western border with Colombia.
The move came amid a standoff between Maduro and opposition leader Juan Guaido over allowing international aid into the country.
Aid collection points have been set up in the Brazilian border state of Roraima, the Dutch Caribbean island of Curacao and at a border crossing near Cucuta on the Colombian border.
Before Maduro announced the border closure, preparations for aid deliveries from Brazil had been half-hearted. It wasn't until Tuesday that the government spokesman Otavio Rego Barros announced Brazil would give the Venezuelan opposition "logistical help" to enable it to collect the aid from the Brazilian border towns of Boa Vista and Pacaraima in the Amazon. However, the spokesman, a former general, stressed that the transport of the goods would be organized and carried out by Venezuelans. The Brazilian media have reported that members of Bolsonaro's Cabinet, especially those from the military, are not in agreement as to how Brazil should participate in the aid deliveries.
Maduro has already ordered the Venezuelan military to block any aid from Cucuta and banned all air and sea travel to and from Curacao.
Venezuelan Foreign Minister Jorge Arreaza wrote on Twitter that the government had warned the Dominican Republic, Puerto Rico and "other Caribbean island countries" against allowing other countries to use their territories for "the planning and organization of actions of an illegal and terrorist nature."
Guaido heading to the border
Guaido has said he would help volunteers transport the aid, much of it medical and food supplies from the United States, across the border near Cucuta on Saturday. He warns that the blockade could cost the lives of some 300,000 people.
Maduro denies that that there are massive food and medical supply shortages in the country. He also accuses the United States of sending aid to try to camouflage plans for a military intervention.
Fifty countries, including Germany, have recognized Guaido as interim president since he openly challenged Maduro. Maduro accuses the opposition leader of attempting a coup with the backing of the United States.
As Maduro and Guaido squabble over the necessity of aid, the situation has grown volatile.
"It can quickly get out of hand," said Luis Vicente Leon, from the Datanalisis survey institute in Caracas. The risk of becoming involved in a conflict with the Venezuelan military is the main reason why the government of Jair Bolsonaro, himself a captain in the reserve forces, is so reluctant to help.
Brazil has a 2,200-kilometer, largely unguarded border with Venezuela.
Additional reporting contributed by Alexander Busch.
amp/sms(AFP, dpa, AP)