Russian Foreign Minister Sergei Lavrov on Friday slammed US sanctions against Venezuela as "illegal" during an official visit to Caracas.
"These sanctions are illegal and are the main cause of the crisis in the Venezuelan economy," said Lavrov after meeting his Venezuelan counterpart Jorge Arreaza.
Russia is one of the main backers of Venezuela's President Nicolas Maduro, along with China and Cuba.
US President Donald Trump has launched a new wave of sanctions against Venezuela's economy, which has been in crisis for years, as well as against Maduro and his ministers.
Among those measures, Washington imposed sanctions on Venezuela's oil industry last year, targeting the country's main source of hard currency, and on Friday it hit its flag airline, Conviasa.
The US administration has said the sanctions are aimed at forcing Maduro to step down.
Juan Guaido, the leader of the opposition who has declared himself Venezuela's rightful president, was a guest at the US Congress when Trump delivered his State of the Union speech earlier this week. He later met with Trump at the White House, receiving the same reception as a head of state.
Washington warned Venezuela against harming Guaido or attempting to block his return to the country.
On Thursday, Elliott Abrams, the US administration's pointman on Venezuela, hinted that Washington is planning to target Russia for backing Venezuela, amid reports that the US could sanction Russian state oil giant Rosneft for its increasingly close relationship with Caracas.
"Russia may soon find out that their continued support of Maduro will no longer be cost-free," Abrams said.
Lavrov, on a tour of South America, did not explicitly mention the US threats against Rosneft, but said that Russia considers "sanctions to be unacceptable, as are attempts to apply the laws of one country to another."
He met with Maduro later in the day.
As Lavrov visited Venezuela, the defense minister of Colombia, the closest US military partner in the region, held talks in Washington.
At a joint news conference, US Defense Secretary Mark Esper made a veiled reference to Russia as he said that Washington was "united" with Colombia.
"This is especially important in an era of great power competition, as our strategic competitors seek dominance and malign influence in regions like Latin America," Esper said.
He said that Maduro's impact on Venezuela has been "shameful."
"We see it urgent that this illegitimate, brutal, oppressive regime led by Maduro needs to move on, and we need to get back to a democracy," Esper said.