Media workers have called for a government investigation into the killings.

A journalist for Pakistan's Geo TV was killed in February in the country's northwest by unidentified men while covering peace negotiations in Swat valley.

'Culture of impunity'

Owais Aslam Ali, a veteran journalist and secretary-general of the Pakistan Press Foundation, told Al Jazeera that the motives for the killing were unclear.
 
"All we see is that a number of journalists have been killed, and nobody has been brought to book," he said.
 
"There's a culture of impunity which exists in Pakistan against attacks on the media, attacks on journalists ... and that is the worrying part of it. Mr Assad is just the most recent casualty."

A report by the group Reporters Without Border says that 2008 was an "annus horribilis" for media workers in Pakistan, with six reporters being killed throughout the year.

Almost 250 others were arrested, and more than 100 incidents were recorded of threats and physical assault against media workers.

The report faulted all sides for the violence, including the Pakistani army, armed anti-government fighters and organised crime.