An Afghan soldier stabbed his teenage sister to death after she rejected a marriage proposal arranged by her family, police said on Tuesday, in what appears to be a so-called “honour killing”.

The 18-year-old woman was killed on Monday in Baharak district of the northeastern province of Badakhshan by her brother, who later fled to a Taliban-controlled area, provincial police spokesman Sanaullah Rohani said.

Rohani said the victim was first strangled by a rope and then stabbed to death.

“Police have launched an operation to arrest him,” Rohani said.

A women’s rights activist from Badakhshan confirmed the murder.

The victim wanted to marry a man she loved but her family wanted her to marry someone else, activist Asifa Karimi said.

“She rejected her family’s proposal and handed herself in to the police, but the police gave her back to her family. Her brother, a soldier, took her home and killed her brutally in a case of honour killing,” Karimi said.

Parts of Afghan society operate under a strict code of “honour” that gives women little or no say in matters such as whom they can marry and whether they can get an education.

Fawzia Koofi, a former lawmaker from Badakhshan, blamed the police for mishandling the case.

Many in Afghanistan, including within the country’s police and judiciary, believe “honour killing” is a suitable punishment for women who elope, Koofi said.

“Women in Afghanistan are still the most vulnerable part of society, not only under the Taliban controlled areas but also in their homes,” she said.