"There were almost 400 people inside the church, but the attackers couldn't get inside the services", Mr Jah said. However, an emergency was declared in all hospitals of the city.
Police guards at the church exchanged fire with the attackers before they could enter the main sanctuary, said local police chief Moazzam Jah.
One attacker set off a suicide vest at the main entrance of the Bethel Memorial Methodist Church, the Washington Post reported. In November, DIG Hamid Shakeel Sabir was killed in a suicide attack while a month earlier a vehicle bomb killed eight policemen.
It was the first time ISIS claimed an attack on a church in Pakistan, though other Muslim extremist groups have targeted churches in the past.
Security forces led congregants out of the church.. "We were in services when we heard a big bang", he told Reuters.
Hospital spokesman Wasim Baig said 57 people were hospitalized in Quetta after the blast. About 60 people were also injured.
Chief of the Army Staff General Qamar Javed Bajwa also strongly condemned the terrorist attack on Quetta church.More news: Royal interview: Prince Harry and Barack Obama rekindle bromance
In October eight people including seven policemen were killed in a terrorist attack.
The COAS commended the effective response by law enforcement agencies, adding, "We stay united and steadfast to respond against such heinous attempts".
Several gunmen have reportedly attacked a Christian church in the southern Pakistani city of Quetta.
A group funeral was held on Monday for the victims in the deadly suicide bombing at the church in Pakistan.
Foreign Office spokesperson Muhammad Faisal condemned the terror attack, saying Pakistan's resolve against terrorism can not be deterred by these cowardly acts of terrorists. Two suicide bombers had tried to enter the church but law-enforcement officials posted outside were able to kill the attackers. He, in his statement of condemnation, said anti-state elements wanted to fan unrest and anarchy in the country to achieve their nefarious designs.
Ahsan Iqbal renewed the pledge that war against terrorism would continue till complete elimination of the menace.