Maduro has come under mounting pressure from Colombia and the United States, which are among more than 50 nations that back opposition politician Juan Guaidó's bid to oust the socialist president. They contend Maduro's re-election in 2018 was bogus.
Tensions spiked recently when Colombia and Venezuela accused each other of harboring hostile armed groups within their borders that are trying to overthrow the neighboring government. In response, Maduro put soldiers on alert and summoned his defense council, saying the machinery of war has started against Venezuela.
"The moment has come to defend our sovereignty and national peace by deploying our defense resources in full force," Maduro said on Twitter.
Roughly 150,000 military personnel will conduct drills through Sept. 28, said Remigio Ceballos, strategic commander of the Bolivarian National Armed Forces, who is overseeing operations.
An array of tanks, missile launchers and aircraft were staged at the Garcia de Hevia International Airport near the border. A military band played as the vehicles filed out.
"This is an operation to defend our national territory," said Ceballos, adding that the armed forces are on the watch to intercept attacks from Colombia, the U.S. or any other threat.
Officials in Washington on Tuesday expressed unwavering support for Colombia during this patch of rocky relations with Venezuela. The two countries have a shared history and their border stretches nearly 1,367-mile (2,200-kilometers).
Carlos Trujillo, the U.S. ambassador to the Organization of American States, said it was "totally unacceptable" that Maduro's "illegitimate government" has threatened the region's security and peace.
"Colombia's allies will do everything possible to help one of the best allies we've had — not only in the Americas but in the world," Trujillo added during a conference call with reporters.
The U.S. special envoy to Venezuela, Elliott Abrams, was even more direct.
"If there are cross-border attacks from Venezuela to Colombia, we can expect Colombians to react," Abrams said. "And obviously, we would fully support Colombia in that situation."
Colombian authorities estimate as many as 1,000 National Liberation Army rebels — or around 40% of that rebel group's fighting force — operate from Venezuela. The rebels there plan attacks like the January car bombing at a Bogota police academy that killed more than 20 mostly young cadets, Colombia says.
For its part, Venezuela's socialist government accuses Colombia's conservative president, Ivan Duque, of allowing training camps to operate inside Colombia for groups that plot violent attacks to undermine Maduro.
This is at least the fourth time so far this year that Maduro has ordered his troops deployed in exercises. In one, Maduro was shown on state TV acting as commander in chief, riding in tanks and jogging in formation with soldiers.
Maduro has maintained support from the military, with the exception of several hundred troops. He's also backed internationally by allies such as Cuba, China and Russia.
Colombia's Duque has said Venezuela should spend its money on food, not missiles.
Associated Press writer Scott Smith reported this story in Caracas and AP writer Luis Alonso Lugo reported from Washington. AP video journalist Luz Dary Depablos in La Fria, Venezuela, contributed to this report.