Two women were among the dead at a Methodist church in the restive southwestern city of Quetta in Balochistan province, said provincial Home Secretary Akbar Harifal.
Several of the wounded were in serious condition, police added.
Officials said police intercepted and shot dead one attacker outside the church before he could detonate his bomb. But the second managed to reach the church’s main door, where he blew himself up.
“Police were quick to react and stop the attackers from entering into the main hall,” provincial police chief Moazzam Jah told AFP.
Each attacker was carrying 15 kilograms (33 pounds) of explosive plus grenades, said civil defense official Aslam Tareen.
Daesh, in a brief statement on its Amaq news agency, claimed responsibility.
Balochistan provincial home minister Sarfraz Bugti said around 250 people normally attend the church on Sundays, but the congregation had swelled to around 400 because it was close to Christmas.
“God forbid, if the terrorists had succeeded in their plans more than 400 precious lives would have been at stake,” tweeted the home minister.
An AFP reporter at the scene saw shattered pews, shoes and broken musical instruments littered across the blood-smeared floor of the church.
Liaqat Masih, a member of the congregation, said he was heartbroken by the violence and feared for his life as the firefight erupted between one attacker and police, who were later reinforced by paramilitaries and regular troops.
“I am devastated to see many of our dear ones dead and wounded today here in front of me,” said Masih, 35.
Hours after the attack reports surfaced that a total of four attackers had been involved, with two escaping.
Senior police official Abdul Razzaq Cheema said investigators were analyzing CCTV footage to check the claim and had launched a search for any further suspects.
Christians make up an estimated 1.6 percent of Pakistan’s 200 million people and have long faced discrimination — sidelined into lowly paid jobs and sometimes the target of trumped-up blasphemy charges.
Along with other religious minorities, the community has also been hit by extremist militants over the years.
Following the latest attack, dozens of Christians protested in the northwestern city of Peshawar and called on officials to protect religious minorities.
In 2013, 82 people were killed when suicide bombers targeted a church in the city.
And last year Lahore suffered one of Pakistan’s deadliest attacks during the Easter season — a suicide bomb in a park that killed more than 70 people including many children.
The bombing was later claimed by the Jamaat ul Ahrar faction of the Pakistani Taliban.
Police and troops have been battling extremists and nationalist insurgencies in mineral-rich Balochistan for more than a decade.
Balochistan, bordering Iran and Afghanistan, is the largest of the country’s four provinces but its roughly seven million people have long argued they do not get a fair share of its vast gas and mineral wealth.
Efforts to promote peace and development have reduced the violence considerably in recent years.
The push includes continuing work on a mammoth Chinese infrastructure project — the China-Pakistan Economic Corridor — which will provide Beijing with a modern-day Silk Road to the Arabian Sea through Balochistan’s deep-sea port of Gwadar.