At least 12 women and children have been killed and more than 20 injured in a suspected bomb attack during a religious ceremony at a Shia mosque in central Pakistan.

Authorities said an explosion tore through the mosque in the western town of Bhakkar, in Punjab province, just before midnight.

They said it appeared that a timed explosive device had been planted inside the women's enclosure of the mosque, where thousands had gathered for the annual ceremony.

Of the injured, 13 were still in hospital while others had been allowed to go home after being treated for shock.

Police suspect the attack is part of the long-running sectarian conflict between extremist groups of the majority Sunni and minority Shia communities.

'Alarming dimension'

A doctor at the local government hospital told the BBC the blast hit almost everyone in the women's enclosure.

"The impact was so powerful, at least two of the bodies have been blown into pieces," he said.

Witnesses spoke of chaos and carnage.

"It was deafening, human bodies flew in the air and there was blood all around," witness Kashif Naqvi told the AFP news agency.

The BBC's Zaffar Abbas in Lahore says this is also the first time that women and children have specifically been targeted, adding a new and more alarming dimension to the conflict.

According to AFP, hundreds of angry Shia youths took to the streets of Bhakkar in protest at the attack, shouting anti-Sunni slogans.

Riot police were deployed and most shops were closed, but residents said tensions were likely to remain high ahead of the funeral processions for the dead.

A protest rally was also held in Islamabad to condemn the government for not providing adequate security to Shias.

The latest incident is the most serious since an attack on a Shia mosque in the city of Rawalpindi earlier this year.

The mayor of Bhakkar town, Khalid Hanif, described the latest attack as an act of terrorism, which, he said was aimed at creating unrest and sectarian friction.

Crackdown

Violence between the Sunni and Shia communities has claimed hundreds of lives across the country in recent years.

Shias account for only about 20% of Pakistan's population.

President Pervez Musharraf pledged tougher action against sectarian extremism in January as part of a broader crackdown on Islamic militants.

He banned five Islamic groups including at least one hardline Sunni organisation traditionally blamed for sectarian attacks.

Since then, more than 30 Shia Muslims have been killed in incidents that had an obvious sectarian dimension.