Disputed Venezuelan President Nicolas Maduro announced the start of military exercises on his country's border with Colombia Tuesday, prompting Washington to promise the Bogota government its "full support."

"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.

Maduro has come under growing pressure from both the U.S. and Colombia, which along with 50 other nations back opposition leader Juan Guaidó as Venezuela's leader. They contend Maduro's reelection in 2018 was bogus.

Tensions spiked recently when Colombia and Venezuela accused each other of harboring hostile armed groups within their borders, intent on overthrowing the neighboring government.

Immediately after Maduro's pronouncement, U.S. Special Envoy for Venezuela Elliott Abrams said that Colombia would have full American support in the case of an attack by terrorist groups or Venezuelan armed forces.

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“The United States is not closer [to a military conflict with Venezuela], but I do worry a lot about the Colombian-Venezuelan border,” said Abrams via videoconference from Brussels, where he had been discussing the Venezuelan crisis with members of the European Union.

Abrams added that U.S. intelligence information has confirmed the presence of the left-wing Revolutionary Armed Forces of Colombia (FARC) and the National Liberation Army (ELN) in Venezuela. Colombian authorities estimate as many as 1,000 ELN rebels — or around 40 percent 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.

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"This is very dangerous because if there are cross-border attacks from Venezuela into Colombia, we can expect the Colombians to react. And obviously, we would be fully supportive of Colombia in that situation," said Abrams. The special envoy reiterated what the Trump administration has said on several occasions, that it is not the current policy of the U.S. government to consider a military response to the feud.

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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 Associated Press contributed to this report.