Maduro argues there is no humanitarian crisis—despite his country’s economic downfall over recent years—and has threatened to close Venezuela’s borders with Columbia and Brazil, both of whom have offered food and medicine, Reuters reports.

According to the BBC, Maduro plans to close the Brazilian border Thursday night.

Still, Guaidó aims to reach the Colombian border by Saturday. The move is likely to result in a showdown with the Venezuelan military, who still remains loyal to Maduro despite Guaidó’s offers of amnesty for defectors.

Guaidó, the president of Venezuela’s National Assembly, declared himself the interim leader last month following demonstrations across Venezuela. Several countries—including the United States—have recognized Guaidó’s leadership, stating Maduro was elected in sham elections, but the president has refused to step down.

Guaidó and other lawmakers departed on buses Thursday morning, beginning the 800-km (500-mile) journey to the Colombian border. They reportedly left among cheers from Venezuelan opposition supporters waving flags but were soon stopped at a roadblock after just 60 miles, where lawmakers scuffled with soldiers in riot gear.

“We have a commitment and that is to reach the border. We will try to get as far as we can,” one lawmaker, Mariela Magallanes, told Reuters. “Humanitarian aid is not the whim of a few lawmakers, it is a necessity.”

Some of the buses, including Guaidó’s, were able to pass through.