Caracas, Venezuela - Venezuela on Monday slammed a US "terrorist" designation of an alleged drug cartel as a "ridiculous lie" amid a major American military buildup in Caribbean waters.

"Venezuela categorically, firmly, and absolutely rejects the new and ridiculous lie from the Secretary of the Department of State, Marco Rubio, who designates the alleged Cartel of the Suns as a terrorist organization... to justify an illegitimate and illegal intervention against Venezuela," the Ministry of Foreign Affairs said in a statement.

The listing of the so-called Cartel de los Soles as a foreign terrorist organization officially took effect on Monday, opening the door to new forms of US pressure on President Nicolás Maduro.

President Donald Trump's administration alleges that the shadowy group is run by Maduro, but has offered little evidence for its accusation – or that it even exists as such.

The designation is part of a major escalation in US hostility towards Latin American countries with leftist governments.

The US has deployed the world's largest aircraft carrier and other military forces in Caribbean waters, supposedly as part of an anti-drugs campaign, but concerns are growing that the Trump administrations means to topple Maduro.

On Saturday, six airlines announced they were canceling flights to Venezuela due to safety concerns.

The US Federal Aviation Administration on Friday urged civilian aircraft in Venezuelan airspace to "exercise caution" due to the "worsening security situation and heightened military activity in or around Venezuela."

US forces have killed at least 83 people in air strikes on boats in international waters since September, according to an AFP tally of publicly released figures.

Despite official claims, no evidence has been made public that drugs were in the boats, while legal experts have pointed out that the strikes would be illegal regardless.