UPDATE 3-Portugal Telecom may sue BES over unpaid family co's debt -sources
* S&P cuts BES rating to B-, warns on solvency risks
* Moody's cuts ESFG to Ca, cites default fears
* Portugal Telecom itself faces potential lawsuit
* BES-linked Rioforte holding company failed to repay $1 bln debt (Adds Portugal Telecom also likely to be sued)
By Sergio Goncalves and Andrei Khalip
LISBON, July 17 (Reuters) - Banco Espirito Santo (BES) could be sued over a loan that one of its founding family's holding companies failed to repay to Portugal Telecom, sources said on Thursday, as credit rating agencies downgraded the bank and its key shareholder.
Still, Finance Minister Maria Luis Albuquerque said the problems faced by BES, Portugal's largest listed bank, and the family's Espirito Santo Group did not pose an imminent danger to the country's financial system and reiterated the government did not plan to use public funds to help the bank.
But other risks loomed for BES following Tuesday's failure by the family's Rioforte company to repay 847 million euros ($1.15 billion) in debt to Portugal Telecom, which forced the telecom firm to take a cut in its stake of a merger with Brazil's Oi.
Sources close to the process told Reuters that Portugal Telecom was considering taking BES to court due to the non-payment as the commercial paper was bought with funds deposited at BES bank accounts, and was considered risk-free by the telecom firm. Continuación...