Secretary of State Mike Pompeo says the U.S. is looking for ways to get humanitarian assistance into Venezuela, after troops loyal to President Nicolas Maduro repelled aid trucks in clashes at the borders with Brazil and Colombia.The top U.S. diplomat, in an interview Sunday on CNN, did not suggest how the U.S. might carry out the aid mission in the face of armed opposition. He said, however, that the United States would consider imposing more sanctions against the Venezuelan government to increase pressure on Maduro to quit in favor of the country's interim president, Juan Guaido, the president of the National Assembly. Guaido is considered by the U.S. and dozens of other countries as the legitimate leader in Caracas.Pompeo called Maduro a tyrant, saying, "I'm confident that the Venezuelan people will ensure that Maduro's days are numbered." U.S. Vice President Mike Pence is meeting Monday with Guaido and other regional leaders in Bogota, the Colombian capital, to discuss a strategy against Maduro and how to get aid into Venezuela, where supplies of food and medicine have run low.Maduro has blocked the aid effort spearheaded by the U.S., saying it is a pretext for an armed U.S. invasion. On Saturday, Maduro supporters fired bullets at those attempting to get aid trucks into Venezuela, while Venezuelan border troops fired tear gas and rubber bullets.Foro Penal [Criminal Forum], a group that tracks violence in Venezuela, reported four deaths at the Brazilian border with Venezuela on Saturday. It said the victims were shot by pro-government militia members.A spokesman for the group, Alfred Romero, posted a video on Twitter saying more than two dozen other people were wounded in the violence. At one border point, aid trucks caught fire, leading the crowd to rush to save the boxes of food and medical supplies. A U.S. State Department official traveling with the Brazilianaid convoy told VOA that the trucks crossed the borderintoVenezuela, but were not allowed through the military checkpoint there, and did notunload their cargo.Afterward, Guaido pressed the case for new foreign assistance to oust Maduro. "Today's events force me to make a decision: to pose to the international community in a formal way that we must have all options open to achieve the liberation of this country that is fighting and will continue to fight," he said on Twitter. The European Union, also supporting Guaido, condemned Maduro's actions to repel the trucks with the humanitarian aid. "We repudiate the use of irregular armed groups to intimidate civilians and lawmakers who have mobilized to distribute assistance," EU foreign policy chief Federica Mogherini said on behalf of the 28-member bloc of countries.Sunday, Pompeo deplored the fact that the Venezuelan military, despite a small number of defections to the opposition, has mostly remained loyal to Maduro."We hope the military will take that role back in protecting their citizens from these tragedies. If that happens, I think good things will happen," he said."We're aimed at a singular mission -- ensuring the Venezuelan people get the democracy they so richly deserve and the Cubans and the Russians who have been driving this country into the ground for years and years and years no longer hold sway," he said.Colombian officials say more than 60 Venezuelan soldiers defected Saturday. Venezuelan Army Major Hugo Parra announced his defection, telling VOA Noticias he recognizes Guaido as the legitimate president of Venezuela.Guaido tweeted his praise of the soldiers' actions. "They aren't deserters," he said. "They've decided to put themselves on the side of the people and the constitution." Maduro announced in a speech to his supporters Saturday that he is cutting off diplomatic ties with Colombia. Colombia President Ivan Duque has been making public appearances with Guaido as they work to transport aid across Venezuelan borders.Duque said Colombian ambassadors and consuls have 24 hours to leave Venezuela.Colombian Foreign Minister Carlos Holms Trujillo released a statement in response, saying, "Colombia holds the usurper Maduro responsible for any aggression or violation of the rights of Colombian officials in Venezuela."Maduro also said he would defend Venezuela's independence with his life. He called Guaido a puppet of the White House.Meanwhile, U.S. President Donald Trump tweeted his support for Guaido."The people of Venezuela stand at the threshold of history, ready to reclaim their country and their future. God Bless the people of Venezuela!" Trump said.