Troops loyal to Maduro block convoys at the Venezuela border.
A US-backed drive to deliver foreign aid to Venezuela met strong resistance as troops loyal to president Nicolas Maduro blocked the convoys at the border.
The forces fired tear gas on protesters in clashes that left two people dead and around 300 injured.
Opposition leader Juan Guaido refrained from asking supporters to continue risking their lives trying to break through the government's barricades at the Colombian and Brazilian borders.
Instead, he said he would meet US vice-president Mike Pence on Monday in Bogota at an emergency meeting of mostly conservative Latin American governments to discuss Venezuela's crisis.
But he did make one last appeal to troops to let the aid in and urged the international community to keep "all options open" in the fight to oust Mr Maduro given Saturday's violence.
"How many of you national guardsmen have a sick mother? How many have kids in school without food," he said, standing alongside a warehouse in the Colombian city of Cucuta where 600 tonnes of mostly US-supplied boxes of food and medicine have been stockpiled.
"You don't owe any obedience to a sadist... who celebrates the denial of humanitarian aid the country needs."
Earlier, Mr Maduro, who considers the aid part of a coup plot and has refused to let it in, struck a defiant tone, breaking diplomatic relations with Colombia.
He accused its "fascist" government of serving as a staging ground for a US-led effort to oust him from power and possibly a military invasion.
"My patience has run out," Mr Maduro said, speaking at a rally of red-shirted supporters in Caracas and giving Colombian diplomats 24 hours to leave the country.
For weeks, US president Donald Trump's administration and its regional allies have been amassing emergency food and medical supplies on three of Venezuela's borders with the aim of launching a "humanitarian avalanche".
It comes exactly one month after Mr Guaido, in a direct challenge to Mr Maduro's rule, declared himself interim president at an outdoor rally.
Even as the 35-year-old politician has won the backing of more than 50 governments around the world, he has so far been unable to cause a major rift inside the military – Mr Maduro's last-remaining plank of support in a country ravaged by hyperinflation and widespread shortages.
Late Saturday, US secretary of state Mike Pompeo called on Venezuelan security forces to "do the right thing" by allowing humanitarian assistance into the country.