Venezuela's military said on Tuesday it was on alert at its frontiers following threats by US President Donald Trump and suspended air and sea links with the island of Curacao ahead of a planned aid shipment.
Opposition leader and self-declared interim president Juan Guaido has vowed to bring aid in from various points Saturday "one way or another" despite military efforts to block it.
But commanders doubled down on their allegiance to President Nicolas Maduro after Trump urged them to abandon him.
"The armed forces will remain deployed and on alert along the borders... to avoid any violations of territorial integrity," said Defense Minister Vladimir Padrino.
Regional commander Vladimir Quintero later confirmed media reports that Venezuela had ordered the suspension of air and sea links with Curacao and the nearby Netherlands Antilles islands of Aruba and Bonaire.
Shipments of food and medicine for Venezuelans suffering in the country's economic crisis have become a focus of the power struggle between Maduro and Guaido.
Aid is being stored in Colombia near the Venezuelan border and Guaido aims also to bring in consignments via Brazil and Curacao, wh9ich is off the coast of Venezuela.
A Brazilian presidential spokesman said the country was cooperating with the United States to supply aid to Venezuela but would leave it to Venezuelans to take the goods over the border.
Maduro says the aid plan is a smokescreen for a US invasion. He blames US sanctions and "economic war" for Venezuela's crisis.
'No safe harbor'
Guaido, the 35-year-old leader of the Venezuelan legislature, has appealed to military leaders to switch allegiance to him and let the aid through.
He has offered military commanders an amnesty if they abandon Maduro.
But the military high command has so far maintained its public backing for Maduro - seen as key to keeping him in power.
"We reiterate unrestrictedly our obedience, subordination and loyalty" to Maduro, Padrino said.
Guaido posted a series of tweets calling by name on senior military leaders commanding border posts to abandon Maduro.
He has branded Maduro illegitimate, saying the elections that returned the socialist leader to power last year were fixed.
The United States and some 50 other countries back Guaido as interim president.
Trump has refused to rule out US military action in Venezuela. He raised the pressure on Monday, issuing a warning to the Venezuelan military.
He told them that if they continue to support Maduro, "you will find no safe harbor, no easy exit and no way out. You will lose everything."
Padrino rejected Trump's threat, branding the US president "arrogant."
If foreign powers try to help install a new government by force, they will have to do so "over our dead bodies," Padrino said.
Venezuela's deputy military attache at the UN announced Tuesday he was siding with Guaido.
"I declare myself to be in total and absolute disobedience to the illegally constituted government of Mr. Nicolas Maduro," Colonel Pedro Jose Chirinos said in a video posted on social media.
Since Guaido declared himself interim president on January 23, he has received the support of an army colonel and an air force general, neither of whom actually have any troops under their command, a retired air force major general and a number of lower-level officers.
'Pack of lies'
Despite sitting on the world's biggest oil reserves, Venezuela is gripped by an economic and humanitarian crisis, with acute shortages of food and medicine.
It has suffered four years of recession marked by hyperinflation that the International Monetary Fund says will reach a mind-boggling 10 million percent this year.
An estimated 2.3 million Venezuelans have left the country since 2015.
Guaido says 300,000 people face death without the aid but Maduro denies there is a humanitarian crisis.
Padrino said the military would not be "blackmailed" by "a pack of lies and manipulations."
Maduro said that 300 tonnes of Russian aid would reach Venezuela on Wednesday. He previously announced the arrival of goods from China, Cuba and Russia, his main international allies.
In a series of tweets, Guaido urged supporters to write to the generals "from the heart, with arguments, without violence, without insults," to win them over.
Battle of the bands
Guaido says he has enlisted the support of 700,000 people to help bring in the aid on Saturday and is aiming for a million in total.
He thanked Britain, France, Germany, Italy and Spain for pledging "more than $18 million for the humanitarian aid."
British entrepreneur Richard Branson said he will hold a pro-aid concert just over the border in Colombia on Friday.
British rock star Peter Gabriel and Colombian pop singer Carlos Vives are among those scheduled to perform.
Former Pink Floyd singer Roger Waters weighed in on Maduro's side in a video broadcast on Venezuelan state media, criticizing Branson and Gabriel and said the aid was being politicized.
Maduro's government plans to stage a rival concert on its side of the border.