The United States military began flying humanitarian aid to a Colombian city close to the Venezuelan border on Saturday in an effort to turbocharge a relief plan that has become a cornerstone of the quest to oust President Nicolás Maduro.

Military personnel used C-17 cargo planes to transport thousands of nutritional supplements and hygiene kits from a base near Miami to Cúcuta, the main staging ground for hundreds of millions of dollars in humanitarian aid that Venezuelan opposition leaders and their international backers hope to get across the border.

Mr. Maduro, who has accused the United States of weaponizing aid, has blocked the main roads that connect the two nations near Cúcuta and put his armed forces on high alert to counter what he called “conspiracies and provocations.”

As the standoff over Venezuela’s future has dragged on for weeks, Mr. Maduro and his foes are vying for the support of the commanders of the armed forces, which so far have remained loyal to the country’s authoritarian leader.