Four people held by the security agencies are being quizzed at an unknown place.

Last Sunday unknown gunmen had attacked president’s chief security officer Bilal Shaikh in Karachi.

Zardari has been under threat from militants for last several years.

Some reports suggest that the same four suspects had planned to kill Zardari in Pakistan Institute of Medical Sciences (PIMS) where his late father Hakim Ali Zardari was admitted.