US Vice-President Mike Pence plans to have his first meeting with Venezuela's Juan Guaido in Colombia on Monday (US time), in a signal of support for the opposition leader after a weekend of violence.
On Saturday, troops loyal to Venezuelan President Nicolas Maduro blocked convoys of US humanitarian aid from crossing from Colombia to Venezuela, using tear gas and rubber bullets and killing four protesters.
The violence could lead the United States to impose new sanctions as early as Monday to cut off the Maduro government's access to revenues.
Pence is travelling to the Colombian capital Bogota to meet with the Lima Group of regional leaders who recognise Guaido as the legitimate leader of Venezuela after Maduro held elections last year which were dismissed as fraudulent.
A senior US official said Pence would be prepared to announce new sanctions at the meeting if the aid was turned back, - adding to pressure from sanctions on state-owned oil company PDVSA.
"If there is any type of violence, or if there is any type of negative reaction from the hierarchy of the Venezuela armed forces, there may also be measures that are announced by the vice-president and other countries in regards to closing even further the international financial circle," the official said before the violence erupted.
The United States and allies are looking at ways to expel family members of Venezuelan military officials who are living outside the country, including some in south Florida, the official said.
Maduro has denied there are shortages of food and medicine in Venezuela, and says the aid is aimed at undermining his government.
Guaido says he will ask the international community to keep "all options open" in the fight to oust Maduro.
Late on Saturday, the opposition leader tweeted; "Today's events have obliged me to take a decision: To propose in a formal manner to the international community that we keep all options open to liberate this country which struggles and will keep on struggling."
Guaido, who declared himself interim president, is recognised as so by the US and some 50 nations.
Throughout the turbulent day, as police and protesters squared off on two bridges connecting Venezuela to Colombia, Guaido made repeated calls for the military to join him in the fight against Maduro's "dictatorship". Colombian authorities said more than 60 soldiers answered his call, deserting their posts in often-gripping fashion, though most were lower in rank and didn't appear to dent the higher command's continued loyalty to Maduro's socialist government.
In one dramatic high point, a group of activists led by exiled politicians managed to escort three flatbed trucks of aid past the halfway point into Venezuela when they were repelled by security forces.
In a flash the cargo caught fire, with some eyewitnesses claiming the National Guardsmen doused a tarp covering the boxes with gas before setting it on fire. As a black cloud rose above, the activists - protecting their faces from the fumes with vinegar-soaked cloths - unloaded the boxes by hand in a human chain stretching back to the Colombian side of the bridge.
"They burned the aid and fired on their own people," said 39-year-old David Hernandez, who was hit in the forehead with a tear gas canister that left a bloody wound and growing welt. "That's the definition of dictatorship."
In all, 285 people were injured and 37 hospitalised on the Colombian side of the border, according to Colombia's foreign minister. At least four were killed on the Venezuela-Brazil border after clashing with pro-government militias.
In the Venezuelan capital, Caracas, the embattled Maduro danced at a pro-government rally, mocked the United States and broke off ties with neighbouring Colombia.
Late in the day, Venezuelan navy vessels threatened to open fire on a ship carrying 200 tons of aid from Puerto Rico, Ricardo Rosselló, governor of Puerto Rico, said in a statement. He said he had ordered the vessels to abandon the area temporarily, decrying the threat as "unacceptable".
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 Guaido, in a direct challenge to 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's so far been unable to cause a major rift inside the military - Maduro's last-remaining plank of support in a country ravaged by hyperinflation and widespread shortages.
