Venezuela is denying that it is the source of an oil spill spread across 2,000km (1,242mi) of Brazilian coastline.
First spotted in early September, oil slicks have now spread around the north and northeastern coast of Brazil, sullying more than 135 points in nine states and damaging regional flora and fauna.
Multiple Brazilian government officials say that analysis of recovered crude indicates a Venezuelan origin.
Venezuela's state-owned PdV and the Opec country's energy ministry denied any link to the country's oil fields.
"We condemn these tendentious claims that seek to deepen the unilateral actions of aggression and blockade against our people," PdV said in a note yesterday in response to a 9 October claim from Brazil's environmental minister Ricardo Salles that the oil "very probably" came from Venezuela.
Salles based his statement on analysis from state-controlled Petrobras, which has denied the crude is from Brazil. An independent analysis from a federal university in Bahia, the most recent state to report oil slicks along its coast, found a "strong correlation" between recovered oil and grades produced by Brazil's northern neighbor.
Cleanup efforts are underway, with around 133 tons of oil sludge already collected, but locating the source of the extra-heavy crude has proved challenging for federal environmental agency Ibama and other groups leading an investigation.
Leading theories mentioned by Brazilian officials are a leaking or sunken tanker, but no corroborating evidence has emerged.
Brazil's rightwing president Jair Bolsonaro has said the leaks could be criminal or the result of a navigation accident.
Brasilia and Caracas were close political allies under former Brazilian presidents Luiz Lula Inacio da Silva and his successor Dilma Rousseff, who was impeached in 2016. Her conservative successor Michel Temer and current president Bolsonaro moved Brazil into the Lima Group of countries that no longer recognize Nicolas Maduro as Venezuela's president.
The Maduro government has so far resisted a US-led campaign to force him from power in favor of opposition leader Juan Guaido.
