KABUL, Afghanistan — Gunmen on Thursday killed one of the most high-profile female police officers in Afghanistan, underlining the threat to women who take on public roles in the country.

Lieutenant Islam Bibi was a well-known face of female advancement, but admitted to receiving regular death threats from people who disapproved of her career — including from her own brother.

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

"She was badly wounded and taken to hospital, and later died in emergency care. Her son was also injured."

Bibi, aged 37 and a mother of three, was seen as an example of how opportunities for women have improved in Afghanistan since the repressive Taliban regime was ousted in 2001.

She was the most senior female officer serving in Helmand, a hotbed of the Islamist insurgency that was launched against the U.S.-backed Kabul government after the fall of the Taliban.

"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.

"He came to see me brandishing his pistol trying to order me not to do it (serve in the police), though he didn't actually open fire. The government eventually had to take his pistol away."

Bibi, a former refugee in Iran, returned to Afghanistan in 2001 and joined the police force nine years ago, saying she signed up for the salary and for the love of her country.

Women's rights are a key focus of international efforts in Afghanistan, with foreign diplomats often pointing to more girls attending school and greater freedom for women as signs of progress.

But donor nations have also raised fears that such advances are at risk as 100,000 NATO troops withdraw next year and Islamist groups lobby for more influence.

Rights groups say the Elimination of Violence Against Women law passed by President Hamid Karzai is a benchmark piece of legislation, though it is poorly implemented and could even be thrown out by parliament.

"Gains on women's rights would be safe-guarded and furthered by promoting and strengthening the implementation of the law," Jan Kubis, the head of UN mission in Afghanistan, said on Wednesday.

"They should not be rolled back under any pretext."

Bibi's death follows the killing of female police Lt. Col. Malalai Kakar, in neighboring province Kandahar in 2008, and the deaths of two successive women's affairs directors in Laghman province within months last year.

In Helmand Thursday a bomb also killed four girls attending a wedding, with officials blaming the blast on Taliban rebels targeting government employees at the event.

The children, aged between seven and 12, died when an improvised explosive device (IED) detonated as they collected water from a river during the celebrations.

Taliban rebels regularly use IEDs to target government officials, and NATO and Afghan soldiers, but civilians and children are also often killed and wounded by the attacks.

According to UN statistics, civilian deaths rose by 24 percent in the first half of 2013 compared to last year.

The United Nations registered 2,499 civilian casualties between January and June, attributing 74 percent to anti-government forces and nine percent to pro-government forces.

Children accounted for 21 percent of all civilians killed and wounded, and casualties caused by IEDs — the Taliban's weapon of choice — had risen 41 percent, it said.