LISBON--Switzerland's financial regulator urged that a Portuguese guarantee to cover losses of bank clients who invested in debt from the collapsed Espírito Santo Group be extended to customers of a Swiss bank, but Portugal's central bank refused to do so, an Espírito Santo official said Tuesday.

Banco Espírito Santo and Swiss Banque Privée Espírito Santo both sold Espírito Santo debt to their customers. They were both part of the Espírito Santo Financial Group, the Espírito Santo company that held financial interests of the collapsed conglomerate.

In a parliamentary hearing, Jose Manuel Espírito Santo, who was the head of Banque Privée Espírito Santo SA in Switzerland, apologized to bank clients who lost their investments after the Espírito Santo group collapsed.

"I'm profoundly sorry for what happened," Mr. Espírito Santo said. Mr. Espírito Santo is the cousin of Ricardo Salgado, the former chief executive of Banco Espírito Santo and the patriarch of the family-controlled group.

Banco Espírito Santo collapsed and was then rescued in August amid a high exposure to the group, which was found to be in a serious financial situation. The group and many of its entities have filed for bankruptcy.

Banque Privée Espírito Santo is in voluntary liquidation.

While Bank of Portugal told Espírito Santo Financial Group to set aside EUR700 million to repay clients of Banco Espírito Santo who had bought the group's debt, it left clients of banks outside Portugal out.

Mr. Espírito Santo said he couldn't comment further on Banque Privée Espírito Santo because the bank is under investigation by the Swiss regulator.

In September, the Swiss Financial Market Supervisory Authority said that it began proceedings that will examine whether Banque Privée Espírito Santo's distribution of securities and financial products violated rules designed to protect clients.

-Write to Patricia Kowsmann at patricia.kowsmann@wsj.com

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