A huge oil spill off Brazil's northeastern coast may have involved a "ghost ship" carrying Venezuelan oil in breach of US sanctions, an expert close to the probe into the disaster said Tuesday.
Brazil has accused its South American neighbor of responsibility for the leakage that began in early September and affects a 2,000-kilometer (1,200-mile) stretch of the Atlantic coast -- charges Venezuela's state oil giant PDVSA denies.
Describing the incident as "very complex and unprecedented," Brazil's navy says it is investigating "lots of hypotheses" for the cause of the massive spill, including a ship accident.
"Yesterday we had a meeting with representatives of various public bodies, such as the environmental agency Ibama, prosecutors and the navy, and this hypothesis of a ghost ship was mentioned," Maria Christina Araujo, an oceanographer at the Federal University of Rio Grande do Norte, told AFP.
"It would be a cargo ship sailing illegally, following little known shipping routes, and would be carrying Venezuelan oil despite sanctions."
Venezuela -- a once-rich oil-producing nation -- is in the grip of an economic crisis and a political standoff between President Nicolas Maduro and opposition leader Juan Guaido.
The situation has worsened with successive rounds of US sanctions against Maduro's government, including steps that have severely curbed its oil exports.
Brazil's Environment Minister Ricardo Salles told a congressional commission last week that the oil "probably came from Venezuela," citing a report from state oil giant Petrobras.
Petrobras, which is involved in the clean-up, has said the oil was "neither produced nor sold" by the Brazilian company.
The oil has appeared in all nine of Brazil's northeastern states -- a poor region with an economy that depends largely on tourism at its picturesque beaches.
So far, nearly 200 tons of oil have been scraped off affected beaches.
Brazil's President Jair Bolsonaro has asserted that the oil spill was the work of criminals.
But Araujo said it was more likely an "accidental leak."
"We have never seen in Brazil a disaster of such magnitude which affects such an extensive area," she added.
At least 13 turtles have been found dead, according to Ibama. The NGO Verdeluz has reported 21 turtle deaths in Ceara alone as a result of the spill.
Tamar, a group dedicated to the protection of sea turtles, has said the leakage was "the worst environmental tragedy" it has encountered since its formation in 1980.