Two attackers targeted a Methodist church in Quetta, but only one managed to detonate his vest, said Sarfaraz Bugti, the interior minister of Balochistan province. The second attacker was shot by a church security guard before he detonated his explosives, Bugti said.
The civilians were killed during the blast and the intense firefight that followed, according to Moazzam Jah Ansari, the provincial police chief. More than 400 people were in the church at the time of the attack, he said.
Bugti tweeted that law enforcement agencies took 16 minutes to complete their operation.
More than two dozen others were wounded, said Wasim Baig, a spokesman for Quetta Civil Hospital, where victims were transported.
The ISIS affilliate in Afghanistan and Pakistan said it was behind the attack. In a text message to CNN, a commander of the affiliate, known as ISIS Khorasan, said that details on the attack and a formal claim of responsibility will be released by the Amaq news agency, the media wing of the terror group.
Pakistan's Foreign Office condemned the attack, tweeting that the nation's "resolve against terrorism cannot be deterred by these cowardly acts."
The defense minister echoed the same sentiment, tweeting that the nation's commitment to
protecting minorities and abolishing terrorism will not change.
Quetta is the largest city and provincial capital of Balochistan province.
Christians make up 2% of Pakistan's population, and face persecution from hardline Islamists, who want to see a strict interpretation of Islamic law take precedence in the legal system.
Previous attacks on Christians include a suicide attack in Lahore that killed at least 14 people in March 2015, and suicide attacks on a church in Peshawar in 2013 that killed more than 80 people.
Attacks by terror groups in the nation are not limited to Christians.
This month, 18 people were killed in a suicide bombing at a Sufi shrine
in southwestern Balochistan. At least 75 people were killed in a suicide attack last February at a packed shrine
in the southern city of Sehwan in Sindh province.