A U.S.-backed drive to deliver foreign aid to Venezuela met strong resistance as troops loyal to President Nicolas Maduro blocked the convoys at the border and fired tear gas on protesters in clashes that left two people dead and some 300 injured.

As night fell Saturday, opposition leader Juan Guaido refrained from asking supporters to continue risking their lives trying to break through the government’s barricades at the Colombian and Brazilian borders. Instead, he said he would meet U.S. Vice President Mike Pence on Monday in Bogota at an emergency meeting of mostly conservative Latin American governments to discuss Venezuela’s crisis.

But he did make one last appeal to troops to let the aid in and urged the international community to keep “all options open” in the fight to oust Maduro given Saturday’s violence.

“How many of you national guardsmen have a sick mother? How many have kids in school without food,” he said, standing alongside a warehouse in the Colombian city of Cucuta where 600 tons of mostly U.S.-supplied boxes of food and medicine have been stockpiled. “You don’t owe any obedience to a sadist … who celebrates the denial of humanitarian aid the country needs.”