
Venezuela's National Guard fired tear gas on residents clearing a barricaded border bridge to Colombia on Saturday, as the opposition began making good on its high-risk plan to deliver humanitarian aid despite objections from President Nicolas Maduro.

By midday, opposition leader Juan Guaido pulled himself on to a truck and shook hands with its driver as he and Colombian President Ivan Duque gave a ceremonial send off to an aid convoy.

The convoy wants to transport nearly 200 metric tons of mostly US-supplied emergency food and medical supplies from the Colombian city of Cucuta.

'Our call to the armed forces couldn't be clearer: put yourself on the right side of history,' said Guaido, in an appeal to troops who constitute Maduro's last-remaining major plank of support in a country ravaged by hyperinflation and widespread shortages.

The opposition is calling on masses of Venezuelans to form a 'humanitarian avalanche' to escort trucks carrying the aid across several border bridges.

Demonstrators push a bus that was torched during clashes with the Bolivarian National Guard in Urena, Venezuela, near the border with Colombia today

Venezuela's National Guard fired tear gas on residents clearing a barricaded border bridge between Venezuela and Colombia on Saturday, heightening tensions over blocked humanitarian aid that opposition leader Juan Guaido has vowed to bring into the country over objections from President Nicolas Maduro

A sergeant of the Venezuela Armed Forces militia who was injured during clashes between the Bolivarian National Guard and demonstrators today

A demonstrator throws back a gas canister while clashing with security forces in Urena, Venezuela on February 23

A demonstrator kicks a burning tire down the street as toxic black smoke fills the air in the Venezuelan town of Urena on Saturday

Reports state that at least one person was injured in Urena after members of the Bolivarian National Guard (GNB, militarized police) clashed with protesters, amid protests over the blockade of the passage between the two countries

A woman moves away from the flames of a burning bus after it was pushed away during clashes with the Bolivarian National Guard in Urena

Clouds of tear gas float in front of a line of Bolivarian National Guard officers who are heavily clad in riot gear on the hot streets of Urena

A citizen kneels before troops with his arms outstretched as rocks and shards of glass spatter the tarmac as violence erupted on the border

Venezuelan officials had ordered the border with Colombia closed after already shutting down crossings from Brazil and the island of Curacao, other points of entry for the aid.

But the residents in Urena defied government orders and began removing yellow metal barricades and barbed wire.

Later, three members of Venezuela's National Guard deserted their posts and solicited help from Colombia.

Colombian migration authorities said they received the request early on Saturday at the Simon Bolivar bridge connecting the two countries.

There was no immediate word on the guardsmen's rank. But a video provided by Colombian authorities show the men wading through a crowd with their assault rifles and pistols held above their heads in a sign of surrender.

The young soldiers were then ordered to lay face down on the ground as migration officials urged onlookers to keep a safe distance.

Demonstrators hurled rocks, set up barricades and burned tires in the Venezuelan border town of Urena, as they sought to test the nerve of the National Guard troops - some of whom broke ranks today.

'Among the troops, whether they are in the army, air force, navy or National Guard, many people disagree (with what is happening),' one of the troops, an officer whose uniform carried the name Linarez, told reporters after entering Colombia, according to another video on social media. 'You can't say anything against the government. It's treason.'

Colombia's migration authority confirmed the defection of the four Venezuelan soldiers.

Leaders of Venezuela's ruling Socialist Party call the aid effort a veiled invasion backed by Washington, and insist that the United States should instead help Venezuela by lifting crippling financial and oil sector sanctions.

Venezuela's opposition says that while the need for basic food and medicines is desperate, the aid operation is also meant to embarrass military officers who continue to support Maduro's increasingly isolated government.

Demonstrators in Urena who blocked roads and burned tires also threw rocks at security forces who responded with volleys of tear gas.

The troops had earlier blocked people from crossing the border into Cucuta, where many Venezuelans now work, shop or send their children to school amid Venezuela's continued economic collapse.

'We were all going to work. We want to work: the people attempted to force their way through,' said Viviana Meza, 29, who works in a Cucuta restaurant.

Guaido, recognised by most Western nations as Venezuela's legitimate head of state, defied court orders not to leave the country when he travelled on Friday to Cucuta, where aid from the U.S. and Colombian governments is stockpiled in warehouses.

Guaido was due to hold a news conference with the presidents of Colombia, Chile and Paraguay in Cucuta on Saturday morning before escorting the aid toward the border on foot.

Demonstrators use large rocks to smash the windows of a bus they commandeered during clashes with the Bolivarian National Guard in Urena

A man who covers his face prepares to launch a rock during heavy clashes with the Bolivarian National Guard today

As others carried missiles, one man carried a crucifix to the border town of Urena as he desperately tried to escape into Colombia

Officers of the National Guard drag this man away from the scene as the town was shutdown on Saturday as troops blocked all movement across the border

A line of heavy trucks packed with aid supplies waited to attempt the crossing, in front of rows of television cameras.

U.S. President Donald Trump's national security adviser John Bolton cancelled plans to travel to South Korea to prepare for a summit addressing North Korea's nuclear program in order to focus instead on events unfolding in Venezuela, his spokesman said on Friday.

'To Maduro's military cronies attacking civilians at the Brazilian border - the world is watching and the perpetrators will face justice,' Bolton wrote on Twitter. 'The Venezuelan military should protect civilians, not shoot them.

Guaido, 35, head of the opposition-run Congress, has provided few details on the transport plan. Trucks are expected to be driven by Venezuelan volunteers and some opposition figures have suggested forming human chains.

Maduro blames the country's dire situation on U.S. sanctions that have blocked the country from obtaining financing and have hobbled the OPEC nation's oil industry.

Concerns about the potential for violence flared on Friday when the Venezuelan army opened fire in a village near the Brazilian border after indigenous leaders attempted to prevent them from advancing, killing a woman and her husband.

The U.S. government condemned the killings.

The U.S. envoy for Venezuela, Elliott Abrams, who travelled to Cucuta on Friday, called them 'a crime and a disgrace', while the U.S. State Department said 'egregious violation of human rights by Maduro and those who are following his orders will not go unpunished.'

Venezuelan Parliament President Juan Guaido greets people from a truck in Cucuta, Colombia today

A young man holds a towel up to his face as he is overcome by the fumes of the tear gas which poured through the air in Urena

A demonstrator gets clothes-lined by a strand of barbed wire as he attempts to dash across the road beside a burning barricade in the road

The man wearing a t-shirt round his face to protect from tear gas lies on the floor not knowing what has hit him after he was caught on barbed wire

Toxic fumes billow from a bus after demonstrators set it on fire, while a line of the National Guard stand across the road in Urena

Venezuelan troops on Saturday morning had blocked the Brazilian border despite protests by villagers in the nearby town of Santa Elena de Uairen who burned a bus, a truck and a National Guard office overnight.

'The situation is critical and we should be all united to allow the aid to pass,' said shopkeeper Jeremy Ortega, 21.

Brazil sent two small trucks with food and medicine to the border on Saturday, after the border closure foiled its plan to have more Venezuelans drive vehicles to pick up the 200 tonnes of aid it has stockpiled in the northern city of Boa Vista.

Brazilian Foreign Minister Ernesto Araujo urged Venezuela's military to let the trucks in.

Nearly 200,000 people attended a benefit concert in Cucuta on Friday featuring Latin pop stars, including Luis Fonsi of 'Despacito' fame, many of whom called on Maduro to step down.

A rival concert held by the ruling Socialist Party on the Venezuelan side was sparsely attended.

Guaido in January invoked articles of the constitution to assume interim presidency and denounced Maduro as a usurper, arguing his 2018 re-election was illegitimate.