Some of the biggest and best-known financial institutions in the world held billions of dollars of Libyan state funds, a leaked report has revealed.
Principal among them were HSBC, Royal Bank of Scotland, Goldman Sachs, JP Morgan Chase, Nomura and Societe General, Global Witness said.
The banks refused to say whether they held, or are still holding, the funds.
All the assets have now been frozen by the European Union and United Nations.
The document, dated June 2010, showed that HSBC held $292.7m (£179.9m) in 10 cash accounts, with a similar amount invested in a hedge fund, while Goldman Sachs had $43m in three accounts.
Almost $4bn was held in investment funds and structured products, with Societe General alone holding $1bn.
Japanese bank Nomura and Bank of New York also held $500m each.
A much larger proportion of Libyan Investment Authority's assets - $19bn in total - were held by Libyan and Middle Eastern Banks, the document revealed.
It also showed that the Libyan Investment Authority (LIA) holds billions of dollars in shares in global corporations such as General Electric, BP, Vivendi and Deutsche Telekom.
It had already been widely reported that the fund held stakes in UK publishing group Pearson, Italy's Unicredit bank and industrial group Finmeccanica, as well as Canadian oil exploration group Verenex.
"It is completely absurd that HSBC and Goldman Sachs can hide behind customer confidentiality in a case like this," said Charmian Gooch, director of campaigning group Global Witness.
"These are state accounts, so the customer is effectively the Libyan people and these banks are withholding vital information from them."
Established in 2006, the LIA holds about $70bn of assets and is the 13th largest sovereign wealth fund in the world, according to the Sovereign Wealth Fund Institute.
The fund, built on Libya's oil wealth, scores two out of 10 on the institute's transparency ranking.
Earlier this month, the EU extended its economic sanctions against Libya to include the LIA and the country's central bank.
It had already frozen assets of Libyan leader Muammar Gaddafi and some members of his family.