COLUMBIA, S.C.  Gov. Mark Sanford of South Carolina acknowledged Thursday that he visited his mistress in Argentina on a taxpayer-financed trade mission to South America early last summer, an admission adding another layer to a scandal that produced increasing calls for his resignation.

“While the purpose of this trip was an entirely professional and appropriate business development trip,” Mr. Sanford said in an e-mail statement issued by his office, “I made a mistake while I was there in meeting with the woman who I was unfaithful to my wife with.”

Mr. Sanford called questions about the trip to Argentina “very legitimate” and said he would reimburse its costs. Documents provided by the South Carolina Department of Commerce suggested that they totaled at least $12,000.

Coming one day after Mr. Sanford confessed that he had spent his week’s absence from the state in Argentina with the woman with whom he had been having a year-old affair, Thursday’s admission was yet another blow to his reputation and led several fellow South Carolina Republican leaders to say he could no longer serve as governor.