The United States on Friday ramped up its attempt to dislodge Venezuelan President Nicolas Maduro from power, imposing new sanctions and revoking visas of senior officials, while opposition leader Juan Guaido toured South America to drum up support. Venezuelan military officials last weekend blocked an opposition-backed effort to bring food into the country via its borders with Colombia and Brazil, leaving two aid trucks in flames and five people dead. Guaido, who is recognized by most Western nations as Venezuela's rightful leader, visited Paraguay on Friday and was due to then travel to Argentina to try to shore up Latin American support for a transition government for the crisis-stricken nation. Guaido's international backers are using a mix of sanctions and diplomacy to pressure Maduro. But Maduro retains control of state institutions and the support of the armed forces, and military intervention is seen as unlikely. "We are sanctioning members of Maduro's security forces in response to the reprehensible violence, tragic deaths, and unconscionable torching of food and medicine destined for sick and starving Venezuelans," U.S. Treasury Secretary Steven Mnuchin said in a statement. The United States "will continue to target Maduro loyalists prolonging the suffering of the victims of this man-made humanitarian crisis." The list includes National Guard Cmdr. Richard Lopez and five other police and military officials based near the Colombian or Brazilian borders. The U.S. State Department later said it had revoked the travel visas of 49 people as it cracked down on "individuals responsible for undermining Venezuela's democracy." Venezuela's Information Ministry did not immediately reply to a request for comment. DefianceSpeaking with Paraguayan President Mario Abdo Benítez, Guaido said 600 members of Venezuela's military had abandoned Maduro's government following the clashes over the aid. Guaido was scheduled to meet with Argentine President Mauricio Macri later on Friday and to travel to Ecuador on Saturday to meet with President Lenin Moreno. Guaido slipped out of Venezuela last week, in violation of a Supreme Court order not to leave the country, to join the aid convoys in Colombia. There, he met with U.S. Vice President Mike Pence and other regional leaders and later traveled to Brazil. He has promised to return to Venezuela by Monday, seen as a form of direct defiance to Maduro, who has said Guaido will eventually "face justice." Governments around the region have called on Maduro to let aid in as inflation above 2 million percent per year and chronic shortages of food have left some eating from garbage bins. Maduro has called the U.S.-backed humanitarian aid effort a veiled invasion meant to push him from power, and has insisted that there is no crisis in the country. Russia has accused the United States of preparing to intervene militarily in Venezuela and, along with China, blocked a U.S. bid this week to get the U.N. Security Council to take action on Venezuela.