The car bomb targeting police and intelligence agency offices killed 35 people, including policemen, civilians and security officers, and injured around 250 others. The May 27 blast damaged buildings in the nearby cathedral compound.
The cathedral premises are home to the Bookshop of the Daughters of St. Paul, St. Anthony Higher Secondary School, Sacred Heart Cathedral High School for Boys and Sacred Heart Cathedral High School for Girls.
The blast shattered several windows and cracked walls in these buildings, a few meters east of the target. However, no students were injured and the schools have been closed indefinitely.
"We were conducting monthly tests and the children had arranged parties in each class that day," said Hadayat Nazar, a Catholic teacher in Sacred Heart Cathedral High School for Boys.
Anxious parents came to collect their children soon after the blast.
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The claim could not be verified and the group's relationship to the Taliban, if any, was unclear, the BBC reported.
The Pakistan military on May 7 launched an anti-Taliban offensive in the northwest, in which a reported 1,200 militants have been killed and at least 2.4 million people forced to flee their homes.
Auxiliary Bishop Sebastian Shaw of Lahore and Vicar General Father Andrew Nisari prayed in the cathedral in the evening after the blast for peace in the country and comfort for victims' families.
Later speaking to UCA News, Bishop Shaw of Lahore condemned the attack on policemen.
"The operation in Swat valley could have been conducted earlier. Now the terrorists have spread throughout the whole country and streets are no longer safe," he said.
The bishop, who resides at the cathedral, recalled that he was going out for a meeting "when suddenly dust gushed from the ceiling of my room."
"I felt vibrations passing through the floor beneath. I rushed out and saw a group of nuns running toward the screaming children in the school. We all thought at that time that a bomb had exploded in one of the schools," the bishop said.
In March last year, the cathedral and its associated institutions suffered heavy damage after a powerful bomb, targeting a government building adjacent to the cathedral, went off.
Meanwhile, the media reports gun and bomb attacks in the northwestern city of Peshawar. Two bombs exploded May 28 in the market, killing six, and another bombing targeted a paramilitary post in the city, killing three soldiers.
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