"Nadeem Mehsud is the brother of a top TTP commander. We have also arrested one of his accomplice," a senior police official said.
Separately, a college principal was gunned down in the city's Liaquatabad area in a suspected targeted killing.
The killing appeared to be sectarian motivated as the deceased Sibt-e-Jaffer, a Shia, did not have enmity with anyone, police said.