A mob killed a seven-year-old and her baby sister along with their grandmother, a member of the Ahmadi sect, after another follower was accused of posting blasphemous material on Facebook, police in Pakistan said.
The dead were part of a religious sect, who consider themselves Muslim but believe in a prophet after Mohammed. A 1984 Pakistani law declared them non-Muslims and many Pakistanis consider them heretics.
The incident is the latest instance of growing violence against minorities in Pakistan.
Police said the violence late on Sunday in the town of Gujranwala, 220 km (140 miles) southeast of the capital, Islamabad, started with an altercation between young men, one of whom was an Ahmadi accused of posting "objectionable material".
"Later, a crowd of 150 people came to the police station demanding the registration of a blasphemy case against the accused," said one police officer who declined to be identified.
"As police were negotiating with the crowd, another mob attacked and started burning the houses of Ahmadis."
The youth accused of making the Facebook post had not been injured, he said.
According to AP, police official Zeeshan Siddiqi said the rioting in the city of Gujranwala erupted after claims an Ahmadi had posted a blasphemous photo of the Kaaba - the cube-shaped structure in the Grand Mosque in Mecca, Saudi Arabia, that observant Muslims around the world face in prayer five times a day.
The photo allegedly contained nudity.
Mr Siddiqi said the victims died of suffocation and that another woman miscarried during the riots and was in hospital.
Under Pakistani law, Ahmadis are banned from using Muslim greetings, saying Muslim prayers or referring to his/her place of worship as a mosque.
Salim ud Din, a spokesman for the Ahmadi community, said it was the worst attack on the community since simultaneous attacks on Ahmadi places of worship killed 86 Ahmadis four years ago.
"Police were there but just watching the burning. They didn't do anything to stop the mob," he said. "First they looted their homes and shops and then they burnt the homes."
The police officer said they had tried to stop the mob.
Accusations of blasphemy are rocketing in Pakistan, from one in 2011 to at least 68 last year, according to the Human Rights Commission of Pakistan.
About 100 people have been accused of blasphemy this year.
