"She was told by her husband that if she delivered another baby girl, he would kill her," Sayed Sarwar Hussaini told German news agency dpa in a Monday report.
"Storay, a 30-year-old mother of three, was choked to death by her husband and her mother-in-law in a remote village in Khanabad district of (northern) Kunduz province," Hussaini said, adding that the mother-in-law has been arrested and police are searching for the husband.
The third baby girl was born three months ago, dpa said.
A 2009 law criminalised 21 acts of violence against women. However, the United Nations in November said that despite the "The 2009 Elimination of Violence against Women" law, the Afghanistan's violence against women is widespread and mostly goes unreported to authorities.