Islamabad, Pakistan (CNN) -- Two 5-year-olds were among five people killed in two blasts across Pakistan on Thursday amid fears of sectarian violence across the country.
At least three people died in an explosion in a Peshawar graveyard. It occurred near a Sufi holy shrine for the sainted poet Rehman Baba.
A boy and girl were among the dead. Seven women and four children were among 21 injured, police said.
Officials fear that the death toll will rise because the blast occurred during a busy time of the week. Militants detonated an explosive in a donkey cart outside a walled compound containing five graves.
In Quetta, two people were killed and 17 others were injured outside a Sunni mosque where people were preparing for prayers, said government official Muhammad Hashim Ghilzai. He said attackers planted a bomb in a sleeping bag near a pillar. It damaged a portion of the mosque and nearby buildings.
The strike comes after a Sunni militant group claimed responsibility for a car bombing Monday on the outskirts of Quetta. At least four people died and 40 others were injured when attackers struck a bus loaded with Shiite students.
There have been many acts of violence and intolerance against religious minorities in the predominantly Sunni nation over the years. Sunni militants who regard other Muslim denominations as heretical have regularly targeted Sufi shrines and Shiite religious processions.
But senior police officials said the attack on the Sunni mosque in Quetta might be a reflection of increasing sectarian violence, in this case an act of revenge.
"This seems to be a retaliation of the bus attack," the official said. He asked not to be named as he is not authorized to speak to the media.
Taliban militants, who are hard-line Sunnis, targeted the Rehman Baba shrine three years ago. A suicide bombing at a Sufi shrine in Punjab province in April 2011 killed more than 40 people.
Attackers targeted Shiites this year. A bomb killed 14 people in a southern Punjab province procession in January. Eighteen others died in February when gunmen opened fire at a bus in the north.
Journalist Ayza Omar contributed to this report.