Islamabad, Pakistan (CNN) Khurram Zaki spent years denouncing Islamic extremists in his homeland. He apparently paid for it with his life.
The Pakistani human rights activist was gunned down at a restaurant in Karachi on Saturday night, fellow activist and lawyer Jibran Nasir said.
The Hakimullah faction of the Pakistani Taliban claimed responsibility for Zaki's death.
"Our four friends in Karachi riding on two motorcycles targeted Khurram Zaki successfully," faction spokesman Qari Saifullah said.
Zaki, 40, was an editor for "Let Us Build Pakistan" -- a blog aimed at supporting "a progressive, inclusive and democratic Pakistan." He was known for condemning radical militants such as the Pakistani Taliban.
"His death is the grim reminder that whoever raises voice against Taliban ... in Pakistan will not be spared," the blog stated Sunday. "And when they have to murder, they never fail."
Who are the Pakistani Taliban?
One of Zaki's most notable acts came after the Pakistani Taliban killed at least 145 people, including 132 children, in the 2014 Peshawar school massacre.
Zaki stood up to radical cleric Maulana Abdul Aziz, who had refused to condemn the attack. The activist led a public campaign against the controversial imam, who revered Osama bin Laden.
"Khurram Zaki took a principled and courageous stance," Zaki's website stated after his death.
The blogger may have predicted his own killing. Zaki had told Nasir that he was getting threats from unknown sources due to his activism, Nasir said Sunday.
Parliamentarian Nafisa Shah mourned Zaki's death.
"Shocked and grieved to learn that a courageous rights activist #KhurramZaki has been killed in targetted attack in #Karachi," Shah tweeted. "Terrible news."
Zaki's death in Pakistan comes after a spate of deadly attacks against Bangladeshi activists.
In the past two years, at least eight atheists and gay rights campaigners have been killed in Bangladesh.
Bangladeshi bloggers speak out despite danger
The situation in Pakistan has become more dangerous in recent years, Human Rights Watch said.
"Pakistani journalists and activists faced an increasingly hostile climate in 2015 due to harassment, threats, and violence from both state security forces and militant groups," the group said in its World Report 2016.