The owner of a mine dam that collapsed in Brazil last month and killed 165 people knew the risk of failure was higher, Reuters claims in a report.
According to an internal news agency report, Vale knew that the Minas Gerais dam violated internal security policies in October.
Vale, the world's leading iron ore miner, said the report was misleading as there were no signs of imminent risk.
Vale previously said the dam had been rated safe by an independent auditor.
"There is no report, study or study that mentions an imminent risk of collapse at Dam 1 at the Córrego do Feijão Mine in Brumadinho," a statement said.
"On the contrary, the dam had all its safety and stability certificates certified by domestic and foreign specialists."
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The incident at the Brumadinho dam is the deadliest mining disaster in Brazil, with many workers still unrecognized and around 300 dead.
It was the second major mining disaster in the region since 2015, when a nearby dam owned by Vale collapsed.
According to Reuters internal report, Vale was told that the likelihood of a collapse in Brumadinho was one in 5,000 – twice as high as the maximum risk allowed by company policies.
The report placed the dam in an "attention zone" where it said that "prevention and mitigation controls" should be applied.
Failure could cost the company $ 1.5 billion (£ 1.2 billion) and lead to more than 100 deaths. In addition, nine other dams located in Vale, Brazil, were classified as vulnerable.
Monitoring the concerns
Vale confirmed the report's existence, but said the causes of the collapse were still under investigation.
An audit of the German company TÜV SÜD, which was carried out in September last year, found that the dam meets the legal requirements.
This review, also reviewed by Reuters, raised a number of concerns, particularly regarding the dam's drainage and monitoring systems.
17 safety recommendations were made, all of which said they were implemented.
It is still unknown what caused the collapse of Brumadinho, but experts believe that liquefaction was responsible.
Liquefaction is a process in which a solid material, such as sand, loses strength and behaves more like a liquid.
Vale's shares increased their losses in New York on Monday after the story was released by Reuters.
Since the January 25 disaster, the company has lost a quarter of its market value – or nearly $ 19 billion.