A small number of clients of the investment banking arm of Portugal's beleaguered Banco Espírito Santo have pulled back from trading with the firm, according to an official of the bank.

At least two clients of Espírito Santo Investment Bank have stopped trading with the bank, the official said. A number of others have expressed concern over the unfolding situation at Espírito Santo International, causing them to "pause for breath" over the past few days, said the official, who spoke on condition of anonymity.