The dispute, which is being heard in Amsterdam after both sides agreed on arbitration, concerns Sonangol's sale 14 years ago of a 40% stake in holding company Esperaza to Exem, which is owned by Isabel dos Santos' husband Sindika Dokolo.

Sonangol argues that Exem acquired the stake on "extremely inconsiderable terms", according to court documents posted on the Amsterdam appeal court's website, where Thursday's ruling was announced.

"There has been no findings of wrongdoing by Exem, Mario Silva (its representative on Esperaza's board), or Sindika Dokolo," Exem said in a statement.

"This ruling gives Exem the opportunity to present the facts while also allowing the company to continue to operate normally," it said.

The dos Santos family has faced legal battles around the world since José Eduardo, who installed two of his children as heads of key state enterprises during four decades of rule, stepped down as Angolan president in 2017.

A representative for Isabel dos Santos said: "Ms. Dos Santos does not head Exem, and has no role whatsoever in Exem or Esperaza and therefore has no involvement in these matters."

For a graphic on Exem and Sonangol:

https://fingfx.thomsonreuters.com/gfx/mkt/xklvyqgozvg/Amorim.JPG

The Angolan government has accused the Dos Santos family of using its influence over government institutions for its own gain.

Isabel dos Santos has repeatedly denied any wrongdoing by the family and says she faces a political "witch hunt" by Angola's new leadership.

The former Sonangol chairwoman lives outside Angola, where her assets were seized last year in an ongoing investigation.

Exem was required to pay 11.3 million euros up front for the stake in Esperaza and the remaining 85%, 63.8 million euros, was financed by Sonangol through loans, court documents showed.

Sonangol later rejected the deal and returned the funds.

"There was no commercial reason to give 40% of the newly acquired Esperaza to Exem," Emmanuel Gaillard of law firm Shearman & Sterling, which is representing Sonangol, told Reuters.

In its ruling, which applies for the duration of the proceedings, the appeals court in Amsterdam froze Exem's stake, removed Exem's representative from Esperaza's board and ordered dividends to be paid into an escrow account.

The court also ordered an investigation into the way in which Sonangol agreed, shortly before Angola's new leadership sacked Isabel Dos Santos in 2017, that Exem's loan repayment could be made in Kwanza, Angola's relatively weak currency.

By Noah Browning