By Sergio Goncalves and Catarina Demony
LISBON (Reuters) - Portugal's market watchdog has launched inquiries into various firms where Angolan billionaire Isabel dos Santos holds stakes, after Angola's chief prosecutor said she could face an international arrest warrant if she fails to cooperate in a fraud investigation.
Angola has named dos Santos, the daughter of former President Jose Eduardo dos Santos, as a suspect over alleged mismanagement and misappropriation of funds while she was chairwoman of state oil firm Sonangol in 2016-2017.
In a statement sent to Reuters, Santos denied any wrongdoing and said she would "seek to clarify our position in relation to the latest accusations".
"I have always operated within the law and all my commercial transactions have been approved by lawyers, banks, auditors and regulators," she said.
In Portugal, Angola's former colonial power, dos Santos holds significant stakes in several important firms.
Gabriela Figueiredo Dias, the head of Portugal's market regulator CMVM, said it had launched inquiries earlier this week into two of those companies, oil company Galp Energia and telecoms firm NOS, and into unspecified auditing firms.
Galp declined to comment and a NOS spokesman said the company had no comment so far.
Angola's chief prosecutor was quoted by Portugal's Lusa news agency as saying late on Wednesday, before traveling to Lisbon on Thursday, that his office sought dos Santos and other suspects "to voluntarily come to face justice".
Failing that, his office would resort to legal instruments at its disposal, one being an international warrant.
Portuguese newspaper Expresso said several people linked to dos Santos were also named as formal suspects, including Nuno Ribeiro da Cunha, director of private banking at small Portuguese lender Eurobic and manager of Sonangol's account at the bank.
Police said on Thursday Ribeiro da Cunha was found dead at the garage of his house in Lisbon on Wednesday night, after apparently committing suicide by hanging. He had tried to commit suicide earlier this month, police said.
No one at Eurobic was immediately available for comment.
Eurobic, in which dos Santos has owned a large stake, said on Wednesday she had decided to sell the stake.
The CMVM regulator said it wanted to find out if there is any relevant information that Galp and NOS should have provided to CMVM but did not.
Figueiredo Dias said hundreds of thousands of files about dos Santos, dubbed the "Luanda Leaks" and released on Sunday, were of "enormous importance" for the market regulator.
The documents were obtained by the International Consortium of Investigative Journalists (ICIJ) and released by several news organizations.
The media reports focused on alleged financial schemes used by dos Santos to build her business empire, including transfers between Angola and Dubai. Dos Santos, who has been living abroad, said on Sunday that allegations made against her were "completely unfounded".
The scandal has led to several resignations, including Mario Leite da Silva, who resigned as chairman of Banco Fomento Angola on Monday, according to a letter seen by Reuters.
Silva, who could not immediately be reached for comment, also stepped down from his position as non-executive board member at Portuguese telecoms company NOS, where dos Santos holds a significant stake.
Two other non-executive board members at NOS resigned on Thursday, the company said in a statement.
Separately, auditors PwC said the firm had "taken action to terminate any ongoing work for entities controlled by members of the dos Santos family" following what it said were "very serious and concerning allegations", and had begun an inquiry.
Dos Santos has said allegations against her are politically motivated.
Authorities in Angola froze dos Santos' assets there in late December.
Asked about dos Santos' case at the World Economic Forum, Angolan Finance Minister Vera Daves told Reuters "we need to send signs to society that we are committed to tackle corruption" and to manage public money and firms well.
President Joao Lourenco, who succeeded dos Santos's father in 2017, has cracked down on the role of his predecessor's children, firing dos Santos from her job chairing Sonangol and her brother from the sovereign wealth fund.
(Additional reporting by Andrei Khalip in Lisbon and Noah Browning in London,; Editing by Frances Kerry and Timothy Heritage)