Brazilian President Luiz Inacio Lula da Silvo on Saturday warned against US military action in Venezuela, saying such a move would spark a "humanitarian catastrophe."
He made the comments at a summit for the five-member South American economic bloc Mercosur, which was taking place at the Iguacu Falls in southern Brazil.
At the same summit, Argentine President Javier Milei hailed Washington's attempts to exert pressure on Caracas.
Venezuela was suspended from the bloc in 2016.
Brazil's left-wing president warned of negative consequences for the Americas if the US was to engage in military operations in Venezuela.
"An armed intervention in Venezuela would be a humanitarian catastrophe for the hemisphere and a dangerous precedent for the world," Lula said in opening comments to the Mercosur summit.
Meanwhile, Milei, who is a close ally of US President Donald Trump and a fierce advocate of austerity and free market reforms, hailed Washington's approach to Caracas.
"Argentina welcomes the pressure from the United States and Donald Trump to free the Venezuelan people. The time for a timid approach on this matter has run out," said the Argentine president, who also attended the summit.
To view this video please enable JavaScript, and consider upgrading to a web browser that supports HTML5 video
The United States has been engaging in a months-long campaign to destroy Venezuelan boats in the Caribbean it accuses of trafficking drugs.
The strikes have killed at least 90 people.
The US government has accused, without providing evidence, the government of Venezuelan President Nicolas Maduro of having links to the Cartel de los Soles criminal organization.
Earlier this week, Trump ordered a blockade on sanctioned oil tankers entering and leaving Venezuela. He has also suggested he could begin targeting sites in Venezuela in air strikes.
In his comments at the Mercosur summit, Lula also called on the European Union to show "courage" and sign a trade deal with the South American bloc.
"Without political will and courage on the part of leaders, it will not be possible to conclude negotiations that have dragged on for 26 years," Lula said.
"We have in our hands the opportunity to send the world an important message in defense of multilateralism, and to reinforce our strategic position in a global environment that is more and more competitive," he added.
The deal has been opposed by groups representing European farmers, especially in France and Italy, which argue that the bloc's agricultural sector would be exposed to unfair competition.