Both is correct, just in an other time form. But usually you said it just few minutes ago and you don't mean a specific time point in the past. " is correct.
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sanyadzAs I have already said...orAs I already said...Thanks in advanceThe more usual one is "As I have already said" because this phrase normally precedes a restatement of something just recently said in the conversation, so it appears to be part of the present situation rather than part of a past situation.