CUCUTA, Colombia (AP) — The Venezuelan military has barricaded a bridge at a key border crossing, issuing a challenge on Wednesday to a U.S.-backed effort by the opposition to bring humanitarian aid into the troubled nation.

The Tienditas International Bridge was blocked a day prior by the Venezuelan National Guard with a giant orange tanker, two large blue containers and makeshift fencing near the border town of Cucuta, Colombian officials said.

The bridge is at the same site where officials plan to store humanitarian aid that opposition leader Juan Guaido is vowing to deliver to Venezuela. The Trump administration has pledged $20 million in aid and Canada has promised another $53 million.

The squabble is now the latest front in the battle between Guaido and President Nicolas Maduro, who is vowing not to let the supplies enter the country. Maduro argues Venezuela isn’t a nation of “beggars” and has long rejected receiving humanitarian assistance, equating it to a foreign intervention.

Roughly 40 countries around the world have backed Guaido, who swore himself in as president in late January contending that as head of the opposition-led National Assembly he is Venezuela’s rightful leader because Maduro’s re-election last year was a sham.

Guaido on Wednesday accused Maduro’s government of rejecting the assistance because officials often handed out imported food and medicine in exchange for bribes.

Maduro has clung to power with the support of Venezuela’s highest-ranking military officers.

He dismisses Guaido as a puppet of the United States, which he says is seeking to colonise Venezuela and exploit its vast oil resources.