Sindh Inspector General of Police A.D. Khowaja on Sunday said that the attempt on Muttahida Qaumi Movement (MQM) leader Khawaja Izharul Hassan's life was "part of a conspiracy to mar Karachi's peace".
The IG also said that police have identified one deceased suspect involved in the attack, calling it a "headway" in the ongoing investigation.
He, however, warned that no speculations should be made about the incident.
Hassan, who is also the leader of the opposition in the Sindh Assembly, escaped an assassination attempt on Saturday when he was returning from Eid prayers.
One of the assailants was killed in the cross fire, along with one of Hassan's guards and a teenager. Four other people were reported to be injured.
Police also said they had recovered a 9mm pistol and a motorcycle used by the killed attacker from the scene of the incident.
MQM Pakistan Farooq Sattar later said in a press conference that the provincial government cannot be absolved of responsibility in the incident.
"What if the leader of the opposition had been killed? What would have the city's situation have been like?" he said. "Already, people are frustrated with the way Karachi was completely neglected in the aftermath of the [recent] rains."
Sindh Chief Minister Murad Ali Shah also condemned the attack and demanded a detailed report from the Sindh IG.