A trove of files was published on Sunday allegedly showing how the daughter of Angola's former president -- dubbed Africa's richest woman -- syphoned hundreds of millions of dollars of public money into offshore accounts.
The New York-based International Consortium of Investigative Journalists (ICIJ) worked with newspapers such as Munich's Suddeutsche Zeitung to reveal the "Panama Papers" tax haven scandal in 2016.
Its latest series called "Luanda Leaks" zeros in on Isabel dos Santos, the former Angola president's daughter.
Angola's prosecutors last month froze the bank accounts and assets owned by the 46-year-old businesswoman and her Congolese husband Sindika Dokolo.
Ms Dos Santos called it a groundless political vendetta at the time.
"Based on a trove of more than 715,000 files, our investigation highlights a broken international regulatory system that allows professional services firms to serve the powerful with almost no questions asked," the ICIJ wrote.
The group said its team of 120 reporters in 20 countries was able to trace "how an army of Western financial firms, lawyers, accountants, government officials and management companies helped (dos Santos and Dokolo) hide assets from tax authorities".
Ms Dos Santos's lawyer dismissed the ICIJ findings as a "highly coordinated attack" orchestrated by Angola's current rulers.
"It is obvious that our client is the subject of a highly coordinated attack on both her reputation and business," the lawyer said in a statement quoted by The Guardian newspaper.
Ms Dos Santos herself told BBC Africa the file dump was part of a "witch hunt" meant to discredit her and her father Jose Eduardo dos Santos.
The former president's daughter headed Angola's national oil company Sonangol. Forbes magazine last year estimated her net worth at $2.2 billion.
Her father's successor Joao Lourenco forced her out of the oil company after becoming president in 2017.
Ms Dos Santos said on Wednesday that she would consider running for president in the next election in 2022.
The ICIJ investigation said Western consulting firms such as PwC and Boston Consulting Group were "apparently ignoring red flags" while helping her stash away public assets.
"Regulators around the globe have virtually ignored the key role Western professionals play in maintaining an offshore industry that drives money laundering and drains trillions from public coffers," the report said.
Its document trove included redacted letters allegedly showing how consultants sought out ways to open non-transparent bank accounts.
One confidential document allegedly drafted by Boston Consulting in September 2015 outlined a complex scheme for the oil company to move its money offshore.
It published a similar 99-page presentation from KPMG.
None of the companies named issued immediate statements in response to the investigation.