Russia has emerged as a key ally of acting President Nicolas Maduro. Two planes, reportedly carrying military supplies and troops, have landed in Caracas.
Two planes loaded with Russian soldiers and military equipment landed in Venezuela at the weekend, officials said.
The delivery is part of ongoing cooperation between the two nations.
What the delivery consisted of
The cargo plane left Venezuela on Sunday.
Read more: What's at stake for Russia in Venezuela?
US Secretary of State Mike Pompeo on Monday called on Russia to "cease its unconstructive behavior," according to the State Department. Its statement did not specifically mention Saturday's reported arrival, but slammed any Russian military support for the "illegitimate regime of [acting President] Nicolas Maduro.
Pompeo also warned his Russian counterpart Sergey Lavrov in a phone call that "the United States [...] will not stand idly by as Russia exacerbates tensions in Venezuela," the statement from his office said.
Lavrov said in a statement that he had criticized what he called "attempts by Washington to organize a coup d'etat in Venezuela" in the call with Pompeo. The statement described such attempts as "violations of the UN charter and undisguised interference in the internal affairs of a sovereign state."
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Key ally: Venezuela's Maduro believes the US is attempting to overthrow the government through military means and install opposition leader Juan Guaido. Russia has emerged as a key ally of Maduro in his efforts to maintain his grip on power.
Previous deliveries: Russia had already sent two Tu-160 strategic bombers to Venezuelain December to support Maduro. Three months ago the two nations held military exercises in Venezuela, which were criticized by Washington as Russian encroachment in the region.
Holding on: Acting President Maduro has refused to step down despite dozens of nations pressuring him to do so. In January, Guaido declared himself interim president, saying elections in 2018 were rigged.
tj, aw/ng (AP, Reuters, AFP)