US Secretary of State Mike Pompeo expressed confidence Sunday that embattled Venezuelan President Nicolas Maduro's "days are numbered," amid a violent impasse over humanitarian aid. "Predictions are difficult. Picking exact days is difficult," Pompeo said on CNN's "State of the Union." "I'm confident that the Venezuelan people will ensure that Maduro's days are numbered." Pompeo's remarks came a day after a US-supported, opposition-led effort to bring humanitarian supplies into the country was repelled by Venezuelan border troops firing tear gas and rubber bullets. Maduro, vowing to "never bow down" at a rally in Caracas, severed relations with neighboring Colombia for supporting the opposition bid. Pompeo blamed armed Maduro loyalists known as "collectivos" for most of the violence at border crossings. "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. The military command has pledged absolute loyalty to Maduro, although some officers and soldiers have deserted, heeding opposition appeals that they switch sides. Pompeo said the United States, which recognizes opposition leader Juan Guaido as the country's interim president, remains committed to bringing in aid. "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.