(Recasts with central bank comments)
LISBON, July 18 (Reuters) - Banco Espirito Santo (BES) should be able to tap private investors if it needs to boost its defences against losses, Portugal's central bank governor said on Friday, reiterating that the lender had sufficient capital reserves.
Recent disclosures of financial irregularities within the Espirito Santo family's business empire have raised questions about potentially destabilising losses at BES, Portugal's largest listed lender, in which the family is the largest shareholder.
"Preliminary contact between BES and international investment banks, as well as interest shown by various entities, investment funds and European banks show that it is very probable that there could be a private solution to reinforcing capital," central bank governor Carlos Costa told a parliamentary committee.
French lender Credit Agricole is the second-largest investor in BES, with a 15 percent stake, but it has said it plans to cut it. The French bank declined to comment on Costa's comments.
A Spanish newspaper reported on Friday that Portugal's central bank was sounding out Spain's Santander and Portuguese lenders about investing in BES.
Santander declined to comment.
BES has said it has 1.15 billion euros ($1.56 billion) in direct exposure to Espirito Santo holdings and has 2.1 billion euros in capital above minimum regulatory requirements to deal with any losses.
But the bank has not been able to quantify the potential losses and is awaiting a restructuring of the Espirito Santo empire to do so.
In the meantime, a key holding company of the clan failed to repay a debt of more than $1 billion to Portugal Telecom this week, forcing the telecoms firm to accept a smaller share of its merger with Brazil's Grupo Oi and reinforcing fears about BES's ability to withstand losses.
Much uncertainty surrounds the bank's business in Angola, where the government in Luanda has guaranteed 4.2 billion euros or nearly 70 percent of its loan book there.
"We are convinced that it will honour its obligations," Costa said of the bank in Angola, adding that the guarantee, "according to our information exceeds the amount of impairments that this loan portfolio could produce".
The misfortunes of the Espirito Santo family, once one of Europe's premier business clans, have sent shockwaves through the region.
Portuguese prosecutors said on Friday they were investigating the family's web of businesses and a group of investors are preparing to file a lawsuit over the unpaid debt of one of its companies.
"The public prosecutor's office is following the situation closely, from the very start collecting all elements that have become public and analysing their penal relevance," it said in an emailed statement to Reuters on Friday.
"There are inquiries under way related to this matter that even pre-date the reports of the past few weeks."
Asked specifically about any investigation of Portugal Telecom's investment in Rioforte, the prosecutor's office would not comment, saying only it was following the Espirito Santo group situation as a whole.
Executives at Portugal Telecom, in which the Espirito family has a significant stake, knew the clan had problems before it lent them the $1 billion in April, people familiar with the talks have told Reuters.
Sources told Reuters PT was considering suing BES due to the non-payment because the debt was bought with funds deposited at BES bank accounts and was considered risk-free by the telecom firm.
PT also faces a lawsuit by several minority investors, expected to be filed on Friday, over its alleged failure to properly gauge the risks of the debt.
"The executive board had to observe the correct distribution of risks, a precaution that they failed to take, which resulted in a suicidal exposure," Octavio Viana, the head of investor association ATM and a representative of the shareholders, told Reuters.
Portugal Telecom has declined to say why it invested so much of its liquidity in one firm's commercial paper. Its merger partner Oi has sharply criticised the Lisbon-based group for not disclosing the loan earlier. Oi's representatives quit the Portugal Telecom board when told of the debt.
BES shares fell 3.5 percent on Friday, adding to losses of nearly 60 percent in the past month, while PT shares plumbed new record lows at 1.72 euros, 2.3 percent lower on the day. ($1 = 0.7394 Euros)
(Writing By Andrei Khalip. Editing by Carmel Crimmins and Will Waterman)