Mr. Johnson’s words were quickly seized upon by Iran-state television and, four days later, by the Iranian authorities, who cited them in a court hearing as proof that she had engaged in “propaganda against the regime.”

Mr. Johnson at first equivocated, saying his remarks could have been clearer and that there was no doubt that Ms. Zaghari-Ratcliffe had been on vacation. But he failed to apologize, prompting a wave of criticism, including calls for opposition lawmakers to call for his resignation.

On Monday, Mr. Johnson addressed Parliament again, this time apologizing for the anguish he had caused the family.

“I acknowledge that the words that I used were open to being misinterpreted and I apologize to Mrs. Zaghari-Ratcliffe and her family if I have inadvertently caused them any further anguish,” he said. “The house should bear in mind that Iran’s regime, and no one else, has chosen to separate this mother from her infant daughter for reasons even they find it difficult to explain or describe.”

Mr. Johnson said that he hoped to meet Mrs. Zaghari-Ratcliffe’s husband, Richard, before traveling to Iran in a few weeks. Mr. Ratcliffe told the BBC this month that he hoped to accompany the foreign secretary to Iran so he could see his wife for the first time in 19 months, but that he was unsure if his request would be accepted.