Local security officials said the police and paramilitary troops rounded up at least 30 terror suspects during cleanup operations in different districts of the volatile city on Thursday, the daily Dawn newspaper reported.
Police also seized arms and ammunitions, including explosives, machine guns and grenades.
The developments come days after Pakistani Prime Minister Nawaz Sharif urged senior leaders of all political parties to help restore peace to Karachi.
However, the Muttahida Qaumi Movement (MQM), the dominant political force in Karachi, says its political figures and activists have been targeted during the ongoing security operations.
Sectarian, political and ethnic violence in Karachi has killed hundreds of people in Pakistan's main commercial hub so far this year.
The Human Rights Commission of Pakistan (HRCP) has said in a recent report that targeted attacks claimed the lives of nearly 1,800 people across the troubled city in the first six months of this year.
The city is home to numerous ethnic groups and has been hit by clashes between rival ethnic and political factions in the past two decades.