Venezuelan opposition leader Juan Guaidó has vowed to open humanitarian aid routes into the country in defiance of the government.
Mr Guaidó, who has declared himself interim president, called on volunteers to help with distribution and said his plans would be ready next week.
Footage shows soldiers blocking a key bridge at the border with Colombia.
A government official called aid “a Trojan horse” and said the country had a duty to defend its borders.
“According to our constitution, we have the right and the duty to defend our borders peacefully,” said Freddy Bernal.
He accused US president Donald Trump, who has endorsed the opposition leader, of just wanting to exploit Venezuelan oil.
Why is aid needed?
Millions of people have fled venezuela as hyperinflation and other economic troubles render food and medicines scarce.
Since the outbreak of the current political crisis, Washington has announced sanctions on the Venezuelan oil industry.
President Nicolás Maduro, who has the support of the army, has rejected letting foreign aid into the country.
Last week a tanker and…