BEIJING — Sweden said it was investigating its ambassador to China after she was accused of arranging unauthorized, secret talks between the daughter of a Swedish bookseller detained in China and two Chinese men who had offered to help free him, but instead pressured her to keep silent.

The back-room talks over the bookseller, Gui Minhai, were held in late January at a hotel in Stockholm, his daughter, Angela Gui, said on Wednesday. She said she grew suspicious of the two businessmen as they asked bizarre questions and offered vague assurances, while wine flowed freely.

Ms. Gui accused the ambassador, Anna Lindstedt, of arranging the talks without authorization from the Swedish Ministry for Foreign Affairs. The ministry said on Wednesday that it had opened an internal investigation into Ms. Lindstedt, and that an interim replacement for her had been installed pending the outcome.

“I placed my faith in a senior official and was rewarded with abuse, threats and an offer of assistance from two men who were clearly unqualified to help and appeared to have other agendas,” Ms. Gui said in an emailed comment about the meeting. “I would like the ministry to explain how this byzantine situation arose.”