Another 50-75 people were reported injured in what police blamed on a suicide bomber at the city of Dera Ismail Khan near Pakistan's lawless tribal areas and touched off a wave of mob violence, The New York Times reported.
The bombing targeted the funeral of a Shiite man who had been shot on Thursday.
Enraged mobs attacked local security forces in the city of about 1 million, ransacked shops and surrounded hospitals as members of the funeral procession sought aid, Mayor Abdur Rauf told reporters.
Rauf said local police officers were overwhelmed and he asked for military assistance. He said the injured were taken to a hospital but there was no doctor on duty, forcing them to shift to a military hospital that could not handle so many.
Dera Ismail Khan has had persistent strife between Shiites and Sunnis with six suicide attacks in recent months.