An Angolan court, acting in a graft investigation, has frozen bank accounts held by Isabel dos Santos, the daughter of former president Jose Eduardo dos Santos, the public prosecutor said.
Dos Santos -- who has been nicknamed Africa's wealthiest woman -- is being investigated with her husband Sindika Dokolo in a corruption affair involving more than a billion dollars (euros), it said in a statement issued late Monday.
The probe is looking at alleged irregularities involving state companies, including the oil giant Sonangol which Isabel dos Santos used to run, and a diamond-marketing firm, Sodiam.
A tribunal in the capital Luanda, in a decision issued on December 23, ordered bank accounts held by the couple to be frozen.
Their holdings in several Angolan companies, including the telecoms firm Unitel and cement company Cimangola, have also been frozen, the statement said.
The court's decision also applies to a Portuguese businessman, Mario da Silva.
In a tweet, Isabel dos Santos, 46, said she sent "a message of tranquility and confidence to my teams."
"We will continue, every day, in every business, doing our best and fighting for what I believe in for Angola. The road is long, the truth will prevail. United we stand strong," she said.
She was appointed head of Sonangol in 2016 but was forced out the following year, in one of the first major acts undertaken by her father's successor, Joao Lourenco.
She has since left Angola -- like most members of the Dos Santos family -- because she claims she has faced death threats.
Jose Eduardo dos Santos ruled Angola for 38 years -- a time widely associated with corruption and nepotism.
His family accuses Lourenco's government of persecution.
The former president's son, Jose Filomeno dos Santos, 41, who is Isabel dos Santos's half-brother, went on trial in early December for alleged corruption.
He is accused of embezzling as much as $1.5 billion from Angola's sovereign wealth fund during his 2013-2018 stewardship.
Despite extensive oil, gas and mineral reserves, the majority of Angolans live in poverty and continue to rely on subsistence agriculture.