The banned radical group Lashkar-e-Jhangvi today claimed responsibility for the deadly suicide bomb attack in Quetta city, Xinhua reported.
At least 54 people were killed and over 100 injured in the attack.
The Punjab-based Sunni group, founded in 1996, also revealed the identity of the bomber, named Rashid Moaawia, 22. He was carrying 15 kg of explosives.
The bomber blew himself up among thousands of people who were participating in a rally in support of the Palestinian people at Meezan Chowk of the city, capital of southwestern Balochistan province. The blast took place at 3.05 pm.
Some 2,500 people were at the rally organised by Shia Muslims.
Police have cordoned off the area and fired into the air to hold back people who tried to enter the blast site in fear of possible attack by angry people who lost their loved ones.
The injured were rushed to various hospitals. Four journalists were also injured.
A widespread protest followed after the blast. Shops were torched and firing in protest was heard across the city.
Pakistan Prime Minister Yousuf Raza Gilani strongly condemned the attack and ordered an immediate probe into the incident.
The attack comes two days after dozens of people were killed in bomb attacks in Lahore. The blast occurred during a rally of Shia Muslims.
A spokesman of Lashkar-e-Jhangvi said on Thursday that Wednesday's attacks were carried out to avenge the killing of their leaders by Shia Muslims. He threatened more attacks.