Portugal has ordered a freeze on bank accounts held in the country by Angola's billionaire former first daughter Isabel dos Santos, who is accused of stealing state funds to build a colossal business empire.

"The public prosecutors have ordered a freeze on the bank accounts following a request by Angolan authorities," a spokesman for Portuguese public prosecutors told AFP.

International media outlets published an inquiry dubbed "Luanda Leaks" on January 19 claiming that Dos Santos fraudulently accumulated fortune estimated at $2.1 billion (1.9 billion euros).

Some 10 Maltese companies were believed to have been used to siphon money out of state enterprises.

She has denied the "unfounded allegations and false claims" and said she has taken steps "to act legally" against the outlets that published them.

Dos Santos, 46, has been living in Europe since President Joao Lourenco fired her as head of the state oil company Sonangol in 2017, soon after he took over from her father.

She has been indicted by Angolan prosecutors for a host of top-level financial crimes, including money laundering and forging documents.

Angola's prosecutor general Helder Pitta Gros visited Portugal, the southern African country's former colonial master, in January to seek the help of Portuguese authorities over the case.

Dos Santos and her associates have huge stakes in several Portuguese firms as well as bank accounts.