Unidentified gunmen have killed a top female police officer in Afghanistan’s restive Helmand province, officials say.

The attack occurred on Thursday when Islam Bibi, a senior policewoman in Helmand province and a mother of three, was on her way to work.

"She was shot by unknown assailants when she was being driven to work by her son in the morning," Omar Zwak, a government spokesman in Helmand provincial told the AFP news agency.

The official said she was badly wounded and taken to hospital where she died in emergency care.

"Her son was also injured,” Zwak said.

Bibi, 37, was the most senior female officer serving in Helmand, a Taliban bastion and had previously received death threats from people who disapproved of her career including her brother.

"My brother, father and sisters were all against me. In fact my brother tried to kill me three times," Bibi told the Sunday Telegraph newspaper earlier this year.

Her killing follows the death of female police officer, Lieutenant Colonel Malalai Kakar, in neighbouring province Kandahar in 2008, and the deaths of two successive women's affairs directors in Laghman province within months last year.