Officials said at least 59 people have been killed and more than 150 other injured.
Most of the casualties were police officers.
Prime Minister Shebaz Sharif visited the mosque, tweeting, “The sheer scale of the human tragedy us unimaginable”.
“While the pain of the grieving families cannot be described in words, I express my heartfelt condolences and most sincere sympathies.
“My message to the perpetrators of today’s despicable incident is that you can’t underestimate the resolve of our people.”
It’s unclear how the bomber was able to make their way into the high-security compound, situated among other government buildings declared a “Red Zone” – housing police and counter-terrorism officers.
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