At least 15 people have been martyred and over 35 others wounded in the bomb attack, which ripped through a Shia procession in Lahore.
The death toll is expected to rise as some of those injured are reported to be in critical condition.
Reports say a bomber driving an explosives-loaded car detonated the bomb when he was stopped at a police checkpoint when trying to enter the procession.
Police and security forces have cordoned off the blast area.
Shortly after the bomb attack, a motorcycle bomb detonated in the southern city of Karachi, causing an unknown number of injuries.
The blast took place in Karachi's densely populated eastern neighborhood of Kala Board.
"When the bomb exploded it was huge and heard far away. Some people have been injured, but we are still collecting details about the blast and wounded," AFP quoted police officials as saying.
Several Shia religious gatherings in other parts of the country, particularly the central province of Punjab, have been targeted over the past some months.
Nearly 40 people were killed and 300 more were injured in the carnage in Lahore last year. The attacks came as Shia Muslims were marking the martyrdom of the first Shia Imam, Ali Ibn-Abi Taleb (PBUH).
Last year, militants claimed responsibility for a deadly attack that killed 43 people at a Shia Muslim gathering in Karachi on Ashura.
Shia Muslims in Pakistan's Kurram Agency have been facing a humanitarian crisis since November 2007, when pro-Taliban militants, who have launched a violent campaign against Shia Muslims over the past years, cut off the area from the rest of the country.
According to local sources, more than 2,000 Shia Muslims have been killed in the region since the start of the campaign by pro-Taliban and al-Qaeda-linked militants.
The pro-Taliban anti-Shia groups are stretching the campaign toward the restive southwestern Pakistan as well.
Quetta, the capital of Pakistan's restive southwestern Balochistan province, has witnessed several instances of violence directed against the Hazara Shia community in recent months.
Shia sources say they make up one-third of Pakistan's population of nearly 160 million. Since the 1980s, thousands of people have been killed in sectarian-related incidents in Pakistan.
Pakistan is also plagued with violence as it is struggling with non-UN-sanctioned US aerial strikes as well as attacks by militants on NATO trucks carrying supplies to the US-led forces in war-ravaged Afghanistan.
Militant attacks, unsanctioned US drone strikes and political unrest have claimed the lives of over 4,000 people throughout Pakistan since 2007.
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