By M Ilyas Khan
BBC News, Karachi
There are few clues as to the identity of the attackers
A Pakistan People's Party (PPP) activist and security chief for party leader Asif Zardari has been killed by unknown gunmen, police and PPP say.
Khalid Shahenshah was gunned down while parking his vehicle outside his house in the southern port city, Karachi.
He was part of Benazir Bhutto's security when she was assassinated in Rawalpindi in December 2007.
The PPP statement has not named any suspects, and the police say there are no eyewitnesses.
PPP officials said Mr Shahenshah returned home after a meeting accompanied by a friend.
The friend went inside the house while he was parking his vehicle in the lane outside.
His friend and a security guard at the residence rushed out when they heard the gunfire.
They saw a white car speeding away but did not see the faces of its occupants, the police said.
The car was apparently abandoned by the assailants in a nearby area and was recovered by the police later.
Mr Shahenshah was with Benazir Bhutto when she was assassinated last year, and was interviewed by the Scotland Yard detectives who investigated the assassination.
The PPP statement described the killing of Mr Shahenshah as "an attempt to disturb the peace" and was done "to weaken the PPP-led government".
The statement advised people to remain calm and "avert the conspiracies of anti-government elements".