A Pakistani police officer says gunmen riding motorcycles have shot and killed a rights activist and wounded two other people in southern port city of Karachi.

Muqaddas Haider says four gunmen on two motorcycles attacked activist Khurram Zaki late Saturday at a roadside restaurant, where he was dining with a friend. The friend was wounded, as was a bystander. Police said Sunday it is not immediately clear who was behind the attack.

Zaki, a former journalist, was best known for helping lead a campaign against Abdul Aziz, the cleric of the Red Mosque in Islamabad, a bastion of Islamic extremists. Zaki and other campaigners filed a court case charging the cleric with incitement against the country's Shiite minority.