At least 36 people have been killed in three separate bomb attacks in Pakistan, in the cities of Karachi, Quetta and Rawalpindi.
The attacks in Karachi and Rawalpindi targeted members of the Shia sect, who were gathering to observe the first ten days of the month of Muharram - the first month in the Islamic calender - on Wednesday.
In Rawalpindi, a twin city to the capital Islamabad, a suicide bomber killed at least 18 people and injured at least 25 others, including several children.
The blast ripped a hole in the walls of a mosque, leaving body parts scattered at the scene.
Hundreds of worshippers, beating their heads and chests, kept marching, even though other explosive devices were found at the site.
Rawalpindi's police chief said that the blast occurred when a suicide bomber entered the procession and the security officials were checking him.
"The suicide bomber blew himself up when the security officials were checking [his body]. We had prior information about the attacks and were fully alert," Azhar Hameed Khokhar said.
Khokhar said that the authorities would run a DNA test of the body parts of the bomber to determine his links.
Another police official, Muhammad Haroon, told AFP news agency that the attack took place when the procession was almost 500m from the mosque where it was heading.
The attacks occurred hours after two bomb blasts killed at least two people near a gathering of Shias in Karachi, Pakistan's commercial hub and its biggest city.
The Pakistani Taliban claimed responsibility for the latest attacks in Karachi and Rawalpindi, a spokesman of the group told AFP news agency.
Kamal Hyder, reporting from Islamabad, said the last 24-hours have been deadly for both Shia worshippers and Pakistan's security forces.
"The attacks in Karachi and Rawalpindi targeted Shia, but the others targeted security forces personnel. The one in Quetta killed three security forces and wounded many more, also including civilians. And another attack in Khyber Pakhtunkhwa also targeted security forces, so it's not just directed against Shia."
Attacks on Shias
The Taliban and other groups have stepped attacks against Pakistan's minority Shia Muslim population in recent months.
Pakistani authorities say they are bracing for the climax of the Shia mourning period at the start of Muharram, which is to fall on the weekend.
Radical groups have staged high-profile attacks on that occasion in the past.
Thousands of security personnel are expected to be deployed in a bid to avoid attacks. About 50,000 people are expected to march through the streets of Islamabad on Saturday, with thousands more expected in Karachi.
The first ten days of Muharram mark the anniversary of the Battle of Karbala, where the grandson of the Prophet Muhammad and his family members were killed.
Earlier on Wednesday, a bomb blast killed at least seven people in the southwestern city of Quetta, security officials said.
The bomb, attached to a motorcycle, exploded near a security vehicle escorting school children, they said. Sixteen people were wounded.
A Reuters news agency reporter saw the bodies of three soldiers under the vehicle as it burned.
There was no immediate claim of responsibility for the attack in Balochistan Pakistan's biggest but poorest province which borders Afghanistan and Iran, and where several armed groups are active.