Police officials said on Thursday that the lynch mob later threw the woman's body into the Kabul River close to the Shah-e-Do Shamshera shrine.

"A woman who had burnt a copy of the holy Koran was beaten by a group of people in the Shah-e-Do Shamshera area," said Farid Afzali, head of the city's police criminal office.

Interior Ministry spokesman Sediq Sediqqi also confirmed the incident, saying that police arrested four suspects in connection with the killing.

Local media identified the woman as 32-year-old Farkhonda. Her family reportedly met the Kabul police's criminal investigation team and said their daughter had been suffering from mental illness for many years.

Progress threatened

Afghanistan has struggled to lift the suppression of women under Taliban rule, which began in the 1990s, but such public attacks, particularly in Kabul, remain unusual.

Since the ousting of militants in 2001, women's rights have made gains, but observers worry that progress is at risk as widespread violence against women persists and women remain under-represented in politics and public life.

According to a 2013 UN report, most violence against women goes underreported, particularly in rural areas.

On Twitter on Thursday, a spokesman for Afghanistan's Ministry of Interior confirmed that four suspects had been arrested in connection with the attack.

Human rights groups have already raised concerns whether enough was done to stop the mob.

"I would certainly hope the government would be trying to arrest and prosecute everyone who was involved and doing an internal investigation into whether the police response was appropriate," said Heather Barr, a senior researcher for women's rights in Asia for Human Rights Watch.

ksb/sms (Reuters, dpa)