New york - Venezuelan President Nicolas Maduro is facing growing international pressure after his troops repelled foreign aid convoys at the country’s borders, with the United States threatening new sanctions and Brazil urging allies to join a “liberation effort”.

Juan Guaido, Venezuela’s self-declared interim president, urged the international community on Sunday to consider “all measures” to overthrow Maduro after clashes at border crossings left at least three protesters dead and 300 others wounded near the Brazilian border.

The opposition leader’s call came in the face of a meeting of the regional Lima Group of nations in Bogota on Monday that will be attended by US Vice President Mike Pence. Pence is set to announce “concrete steps” and “clear actions” at the meeting to address the crisis, a senior US administration official said on Sunday, declining to provide details.

The US last month imposed crippling sanctions on the OPEC nation’s oil industry, squeezing its top source of foreign revenue.

US Secretary of State Mike Pompeo said he was confident that “Maduro’s days are numbered,” blaming the border violence on armed supporters known as “colectivos”.

“We’re aimed at a singular mission - ensuring the Venezuelan people get the democracy they so richly deserve,” he said on CNN’s State of the Union programme on Sunday.

President Donald Trump has in the past said military intervention in Venezuela was “an option”, and following the Venezuelan opposition’s failure to penetrate government blockades, some in Washington stepped up the belligerent rhetoric. US Senator Marco Rubio, an influential voice on Venezuela policy in Washington, said the violence on Saturday had “opened the door to various potential multilateral actions not on the table just 24 hours ago”.

Later, he tweeted out pictures of anti-American politicians including Panama’s Manuel Noriega, Libya’s Muammar Gaddafi and Romania’s Nicolae Ceausescu at the height of their power and then brutal downfall, in a not-so-subtle suggestion being that Maduro himself could suffer a similar fate.

Meanwhile, Brazil, a diplomatic heavyweight in Latin America which has the region’s largest economy, called on “the international community, especially those countries that have not yet recognised Juan Guaido as interim president, to join in the liberation effort of Venezuela.”

Colombia’s President Ivan Duque in a tweet denounced Saturday’s “barbarity”, saying Monday’s summit would discuss “how to tighten the diplomatic siege of the dictatorship in Venezuela”.

Maduro, who retains the backing of China and Russia, which both have major energy sector investments in Venezuela, says the opposition’s aid efforts are part of a US-orchestrated coup.

His information minister, Jorge Rodriguez, during a news conference on Sunday gloated about the opposition’s failure to bring in aid and called Guaido “a puppet and a used condom”. Cuban President Miguel Diaz-Canel said on Sunday that Venezuela, the Caribbean island’s top ally, was the victim of US imperialist attempts to restore neoliberalism in Latin America.

Foreign aid, much of it from the US, has become the centrepiece of the standoff between Maduro and Guaido.

The 35-year-old Guaido has won the backing of more than 50 governments around the world since declaring himself interim president at a rally in January, arguing that Maduro’s re-election last year was illegitimate because some popular opposition candidates were barred from running.

But he has so far been unable to cause a major rift inside the military, despite repeated appeals and the offer of amnesty to those joining the opposition’s fight for power.

On Saturday, trucks laden with US food and medicine on the Colombian border repeatedly attempted to push past lines of troops but were met with tear gas and rubber bullets.

Two of the aid trucks went up in flames, which the opposition blamed on security forces and the government on “drugged-up protesters”.

The Brazilian border state of Roraima said the number of Venezuelans being treated for gunshot wounds rose to 18 from five in the past 24 hours; all 18 were in serious condition.

That was the result of constant gun battles, which included armed men without uniforms, throughout Saturday in the Venezuelan town of Santa Elena, near the border.

The Venezuelan Observatory of Violence, a local crime monitoring group, said it had confirmed three deaths on Saturday, all in Santa Elena, and at least 295 injured across the country.

Emilio Gonzalez, mayor of Gran Sabana, the district in which Santa Elena is located, told reporters the death toll could be as high as 25.

In the Venezuelan city of Urena on the border with Colombia, streets were still strewn with debris on Sunday, including the charred remains of a bus that had been set ablaze by protesters.

UN Secretary-General Antonio Guterres appealed on Sunday for “violence to be avoided at any cost” and said everyone should lower tensions and pursue efforts to avoid further escalation, according to his spokesman.

The European Union has also condemned the use of violence and armed civilian groups to block the entry of aid.

“We repudiate the use of irregular armed groups to intimidate civilians and lawmakers who have mobilised to distribute assistance,” said Federica Mogherini, EU foreign policy chief.