Image copyright White Star Image caption Sabeen Mehmud had been the subject of threats before being killed in Karachi

A leading Pakistani human rights activist has been killed in a drive-by shooting in Karachi after hosting a talk on allegations of torture in the province of Balochistan.

Sabeen Mehmud was shot dead as she drove home with her mother, who was also attacked.

Ms Mehmud had been the subject of death threats before.

Tributes were paid to her on social media as soon as news of her death emerged.

Ms Mehmud was a director of the charity The Second Floor, also known as T2F.

T2F regularly holds seminars on human rights issues. It houses a cafe and book shop where Karachi's liberal activists and students can meet.

The seminar on torture in Balochistan was held at T2F, having been cancelled by university authorities in Lahore, where it had been due to take place in the last few weeks.

Taliban militants, Baloch separatists and other groups fight in Balochistan, which borders Iran.

Shortly after leaving the event, Ms Mehmud and her mother were shot. Pakistan's Dawn newspaper reported that Ms Mehmud died on her way to hospital, and that she had been shot five times.

Dawn reported that her mother is in a critical condition in hospital.

'An extraordinary life' - by Fifi Haroon, BBC Urdu

When you don't see that many people stand up, and you do, you are very likely to stand out. Sabeen knew that and went ahead and did it anyway.

It's a huge thing when you have been told to call off an event, only to go ahead and do the same event in a public space, when it's so dangerous in Pakistan.

It is difficult to believe someone so vibrant, so alive, so determined is gone. There is a disbelief in Pakistan, on social media and from young people.

To me, she was someone who could have chosen to lead a very different, ordinary life. But she chose to lead an extraordinary life.

Within an hour of the attack, tributes had started appearing on social media.

Image copyright Twitter

Image copyright Twitter

Image copyright Twitter

Among the tributes was one from Siraj ul Haq, the head of the conservative Islamist group Jamaat-e-Islami, who tweeted: "Murder of Sabeen Mahmud is shocking & horrific. It is extremely condemnable, indeed coward of them to target a woman."

No group has yet said it carried out the attack, though Ms Mehmud is believed to have been the subject of threats by the Pakistani Taliban in the past.

Image copyright Instagram Image caption Sabeen Mehmud posted a photograph from inside Friday's talk shortly before being attacked

Ms Mehmud set up T2F having already established a charity, PeaceNiche, in Karachi. She said she "maxed out seven credit cards" to keep the centre going.

She also helped promote the importance of learning computer skills among Pakistani youth, and hosted hundreds of events at T2F.

In a profile in a Pakistani media magazine in 2013, Ms Mehmud was asked what her superpower would be. She answered: "I'd like to wave my magic wand and de-weaponise Karachi."