By Agence France-Presse
Self-declared interim president Juan Guaido called on the international community to consider "all measures to free" Venezuela after clashes at the border crossing left at least two people dead.
Guaido announced he would participate in Monday's Lima Group meeting of mostly Latin American countries in Bogota, and called on the international community to be prepared for "all possibilities" regarding Maduro. US Vice President Mike Pence will represent Washington at the meeting.
Secretary of State Mike Pompeo said the United States "will take action" as he condemned violence perpetrated by Maduro's "thugs." President Donald Trump has said that Washington is not ruling out armed action.
Humanitarian aid, much of it from the United States, has become the centerpiece of the standoff between Maduro and Guaido, the 35-year-old leader of Venezuela's National Assembly who declared himself interim president one month ago.
The country is gripped by a humanitarian crisis that has seen poverty soar during a prolonged recession and hyperinflation.
Maduro claims the aid is a smokescreen for a US invasion, and has ordered several crossings on Venezuela's borders with Colombia and Brazil closed.
Two people, including a 14-year-old boy, were killed in clashes Saturday with Venezuelan security forces that left more than 300 people wounded at various border posts.
Guaido had set a Saturday deadline for delivering food and medical aid stockpiled in Colombia and Brazil.
Hundreds of Venezuelans, many dressed in white, were frustrated in their attempts to collect the aid at the Colombian border, where they were pinned back by Maduro's security forces.
Trucks with aid were prevented from entering the country, and force was used to keep out Venezuelan nationals trying to cross in from Colombia carrying aid parcels.
Colombia ordered aid trucks to return from the border after the violence.
International aid is also being held on the Caribbean island of Curacao.
A ship with aid from Puerto Rico was forced to turn back after receiving a "direct threat of fire" from Venezuela's military, the governor of the US territory Ricardo Rossello said. He slammed the move as "unacceptable and outrageous."
- Violent clashes -
Since dawn, protesters in the border towns of Urena and San Antonio were kept at bay by the Venezuelan National Guard firing tear gas and rubber bullets.
Gunshots could be heard in the streets of Urena during hours of rioting. Civil defense officials in Colombia said at least 285 people had been wounded in clashes at border bridge crossings.
But the most serious incident came hundreds of miles (kilometers) away, at the Santa Elena de Uairen crossing point on the southern border with Brazil where the killings took place.
Another 31 people were wounded when Venezuelan troops opened fire on civilians hoping to collect aid across the border with Colombia, according to rights group Foro Penal.
Maduro's supporters also halted and set ablaze two trucks loaded with aid driven through barricades on a border bridge, sending a pall of black smoke into the sky over the Santander crossing linking Cucuta and Urena.
Two other trucks carrying aid sent by Brazil to Venezuela returned to the Brazilian city of Paracaima after Venezuelan troops barred them from crossing for several hours.
Some Venezuelan National Guard troops however took advantage of the confusion to abandon their posts and cross into Colombia. Guaido has offered amnesty to all security personnel switching sides.
Colombia's immigration service said at least 60 members of the armed forces had deserted the "Maduro dictatorship" by late Saturday.
Guaido -- recognized as interim leader by more than 50 countries -- formally launched a long-planned distribution operation at a warehouse at the Tienditas border bridge in Cucuta joined by the presidents of Chile, Colombia and Paraguay.
Angered by Colombia's support for Guaido, socialist leader Maduro announced that Caracas was severing diplomatic ties with Bogota, and gave Colombian diplomats 24 hours to leave the country.
"I will never bow down, I will never give in. I will always defend our country with my own life if necessary," Maduro told a rally of his supporters in Caracas, after thousands had marched through the city under the slogan "Hands off Venezuela."
At a separate Caracas rally thousands of government opponents, mostly dressed in white, marched waving flags outside the La Carlota military airport.
As many as 300,000 Venezuelans are in dire need of food and medicine after years of shortages and malnutrition, according to Guaido, who has accused Maduro of rigging his re-election and is demanding a new vote.
United Nations figures show that 2.7 million people have fled Venezuela since 2015 and around 5,000 Venezuelans emigrate each day.