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.
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 cargo containers blocked the Simon Bolivar International Bridge, which links Venezuela to its more stable neighbour to the west.
The blockages were still there on Friday, and many soldiers were seen standing guard.
Mr Guaidó does not control any territory in Venezuela so, instead, he is planning to set up collection centres in neighbouring countries to which Venezuelans have fled.
He said he wanted to set up an international coalition to gather aid at three points, and press Venezuela's army to let it into the country.
Food and medicine organised by the US federal government's USAID agency arrived on Thursday and have been stored at a warehouse on the Colombian side of the border.
Mr Guaidó has warned many Venezuelans are in danger of dying without international aid.
A number of Venezuelan leaders have also appealed to the military to allow aid lorries to cross into the country.
What's the background to the crisis?
In January, Mr Maduro was sworn in for a second term following disputed elections which many opposition leaders did not contest because they were in jail or boycotting them.
Mr Guaidó, who is head of Venezuela's National Assembly, declared himself president on 23 January.