BEIRUT, Lebanon — The Lebanese authorities have detained a daughter of Abu Bakr al-Baghdadi, the leader of the Islamic State extremist group, as well as the child’s mother, American officials said Tuesday, possibly granting Lebanon leverage in its efforts to free Lebanese captives held by the group.

Lebanese security officials had reported earlier that Mr. Baghdadi’s wife and one son had been arrested more than a week ago while trying to enter Lebanon from Syria. But American officials said that the child was a girl and that it remained unclear whether her mother was Mr. Baghdadi’s legal wife, common-law wife or former wife.

The arrests appeared to be the first time that one of the governments that have battled the Islamic State had taken into custody any relatives of the jihadist leader, who has not been seen in public for months. The detentions raised the possibilities that the woman could provide valuable information on the group’s operations or be used as a bargaining chip in hostage negotiations.

Asked about the reports in Brussels, Secretary of State John Kerry said that he did not know the details of the case and that the United States would not take part in such talks.