Unitel sued dos Santos' Dutch company Unitel International Holdings (UIH) in 2020 over loans that were provided in 2012 and 2013, when dos Santos was a director of Unitel, to fund UIH's acquisition of shares in telecoms companies.

The loans were not repaid and around $395 million plus interest remains outstanding, Unitel's lawyers said on Tuesday.

The two companies are not related despite having the same name and dos Santos, who owns UIH, resigned as a director of Unitel in 2020.

Unitel had applied to personally add dos Santos - Africa's first female billionaire, whose father Jose Eduardo dos Santos ruled Angola for 38 years until 2017 - to its case against UIH.

Judge Mark Pelling ruled on Thursday that dos Santos should be added to the existing lawsuit.

He said Unitel has a "realistic prospect of success" in relation to its allegations that dos Santos breached her duties as a director of Unitel.

Dos Santos "vehemently denies that she has breached any of her director's duties", her lawyer Richard Hill said in court filings on Tuesday.

Her lawyers also argue that Unitel is responsible for UIH's inability to pay, because of its alleged role in the "unlawful seizure by the Angolan state of UIH's assets". Unitel denies any involvement in the asset seizure.

Dos Santos has faced corruption accusations for years, including allegations by Angola that she and her husband steered $1 billion in state funds to companies in which they held stakes during her father's presidency, including oil giant Sonangol.

Around $1 billion of her assets in Angola were seized last year, while other assets linked to her have been seized in Portugal.

Dos Santos, who says she lives in Dubai, has repeatedly denied any wrongdoing and her lawyers have described the allegations against her as part of a "political conspiracy".

(Reporting by Sam Tobin; Editing by Susan Fenton)

By Sam Tobin