Mr Forsyth faced three complaints of inappropriate behaviour towards female staff before leaving Save the Children, the BBC reported this week.
He was accused of sending inappropriate texts and commenting on what young female staff were wearing.
He said he "apologised unreservedly" to the three workers at the time.
Mr Forsyth said the reason for his resignation as Unicef's deputy director was not because of what he described as the mistakes he made in his former role at Save the Children.
