During a visit to the Colombian border city of Cucuta, Sen. Marco Rubio warned Venezuelan soldiers that they would commit a "crime against humanity" if they blocked the entry of U.S. aid being channeled through rivals of disputed socialist President Nicolás Maduro.

The Florida Republican made a stop in Cucuta on Sunday, where U.S. aid packages were being stockpiled for distribution by opposition leader Juan Guaido, who is recognized by the U.S. and dozens of other countries as Venezuela's legitimate president.

Maduro has been using troops to block aid from entering, saying it's unnecessary and part of coup to overthrow him.

Venezuelans fleeing hardship at home have rushed into Cucuta seeking food and medicine in recent months. Rubio told a cheering crowd that Venezuelan soldiers who blocked aid would spend "the rest of their lives hiding from justice."

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During a contentious hearing before the House Foreign Affairs Committee, the U.S. special envoy for Venezuela, Elliott Abrams, told members of the committee that while the Trump administration has preferred to use economic, humanitarian and diplomatic channels to deal with the Maduro regime, the use of military force is not being ruled out.

“When we say all options are on the table, that is because all options are on the table,” Abrams said, adding that military force “is not the preferred route and not the route we’re going down.”

The comments on Capitol Hill by Abrams came as President Trump met last week in the Oval Office with Colombian President Ivan Duque. The two leaders discussed, among other issues, the humanitarian crisis in Venezuela that has sent an estimated 1.14 million refugees into Colombia.

Despite having the world's largest oil reserves, Venezuela is gripped by widespread malnutrition, disease and violence after 20 years of socialist rule launched by the late President Hugo Chávez. Critics have accused Maduro, Chávez's hand-picked successor, of unfairly winning an election last year for a second six-year term by banning his popular rivals from running and jailing others.

The U.S. and other nations have demanded Maduro step down and have recognized National Assembly leader Guaido as Venezuela's rightful leader. Venezuelans also have staged large protests to pressure Maduro to leave.

Venezuela's opposition has called its supporters into the streets across the country in a campaign to break the military's support of Maduro, while Maduro has rallied supporters to demonstrations following over a month of pressure led by Guaido.

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"Right now, I'm going to give this order to the armed forces: Allow in the humanitarian aid. That's an order," Guaido told the mass of people gathered in Caracas.

Guaido said last week that he would try to run caravans of badly needed food and medicine into Venezuela -- but it wouldn't start for nearly two weeks.

The Associated Press contributed to this report.