LISBON/JOHANNESBURG/LAGOS (Reuters) - Angola has frozen the assets of Isabel dos Santos, the billionaire daughter of the country’s previous leader, in a sign that President João Lourenço is taking a tougher line against the former first family.

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Since ending José Eduardo dos Santos’ nearly 40-year grip on power in 2017, Lourenço has been trying to erase the influence of his predecessor and reform sub-Saharan Africa’s third-largest economy. But Lourenço is under pressure as the economy continues to contract under his watch.

Isabel dos Santos said the asset freeze was “politically motivated” and that the case against her had been held in total secrecy.

“The judgment contains statements which are completely untrue,” she said in a statement. She later told Reuters by phone that she had never been summoned or questioned by an Angolan court or prosecutors.

The move against her comes as the ex-president’s son, José Filomeno de Sousa, faces corruption charges, accused of helping transfer $500 million from the sovereign wealth fund.

Called “Africa’s wealthiest woman”, Isabel dos Santos amassed a fortune estimated at more than $2 billion through stakes in Angolan companies including banks and the telecoms firm Unitel, earning her the nickname “the Princess”.

She chaired the state oil company Sonangol before being sacked by Lourenço months after he came to power.

A court document dated Dec. 23 said the government believed Isabel dos Santos, her husband Sindika Dokolo and Mário Leite da Silva, chairman of Banco de Fomento Angola (BFA), had caused the state losses of more than $1 billion.

“The state through its companies Sodiam (a diamond marketing firm) and Sonangol transferred enormous quantities of foreign currency to companies abroad whose beneficiaries are the defendants, without receiving the agreed return,” the court said. “The defendants recognize the existence of the debt but allege that they do not have the means to pay.”

Dokolo told Reuters the Angolan government was pushing for a freeze on his and his wife’s international assets as well. He said Lourenço’s government was trying to portray him and his wife as criminals without proper evidence. Da Silva declined to comment.

The asset freeze applies to personal bank accounts of dos Santos, Dokolo and da Silva in Angola and stakes they hold in Angolan firms including Unitel, BFA and ZAP MIDIA. Dos Santos is believed to live in Portugal and Britain and to have a significant portion of her wealth offshore.

The court said the central bank would ensure that no funds leave the Angolan bank accounts of the three accused.

The boards of each of the nine Angolan companies affected by the asset freeze must ensure that the relevant stakes are not sold and that no profits from the shares are transferred to the accused.

The court said Isabel dos Santos had tried to transfer some of her businesses to Russia and that Portuguese police had blocked a transfer of 10 million euros ($11 million) from one of her business partners to Russia.

Darias Jonker, Africa director at Eurasia Group, said the asset freeze showed Lourenço felt he could now move aggressively against the dos Santos family without risking his control over the ruling MPLA party.

“The key prize is the neutralization of Isabel dos Santos,” Jonker said.