City Police Officer Mir Zubair Mehmood said that at least 29 people were killed in the blast in a crowded area 40 to 50 metres away from Abu Talib Imambargah at the Shia-majority Hazara town.
Mehmood said the dead included nine women as well as four children.
He said suicide bomber was stopped at the entrance of the Imambargah by policemen and volunteers as he tried to enter the building and then blew himself up.
He said bomb disposal squad was also investigating that the second blast was caused by a remote controlled bomb.
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Mehmood said the suicide bomber whose severed head had been recovered from the site had come on a cycle alone.
The blasts caused damage to the shops and nearby buildings as well.
"It was an attack targeting Hazara Shia community," he said.
The dreaded and outlawed Lashkar-e-Jhangvi (LeJ) claimed responsibility of the attack, saying that the first attack was a suicide blast while the second was carried out by a remote-controlled device.
In February this year two blasts in the Kirani market of the town killed atleast 100 people and injured dozens.