At least one child was killed and dozens of people were wounded in a drive-by bomb attack at a Shi'ite mosque in Karachi, police said.
Police said two men on a motorcycle lobbed the bomb as women and children sat outside the mosque in the Pakistani port city's densely populated Liaquatabad district.
Radical Sunni Islamists periodically target mosques frequented by minority Shi'ites, whom they see as infidels. Shi'ites make up about a fifth of Pakistan's mainly Sunni population of around 180 million.
"One boy has expired and another boy and a woman are in critical condition," Karachi police chief Mushtaq Meher told Reuters.
No group immediately claimed responsibility for the attack.
Soon after the blast, Shi'ite men and woman gathered outside the mosque and chanted slogans to protest about the lack of security provided to them in the Islamic month of Muharram.
That marks the time when Shi'ite Muslims around the world frequent mosques to mourn the slaying in battle of Prophet Mohammad's grandson Imam Hussein.
The government pledged to crack down on all militant groups following the December 2014 massacre of 134 children at an army-run school in the northwestern city of Peshawar.
It has reintroduced the death penalty, set up military courts to speed convictions and widened its military campaign in lawless tribal areas.
But Pakistan's religious minorities, among them Shi'ites, Ahmadis, Christians and Hindus, say the government is still doing little to alleviate their daily struggle against discrimination and violence.