Accusations of military interference, encroaching extremism and a series of deadly attacks have cast an alarming shadow over Pakistan's hopes for a rare democratic transition of power in next week's election.

Observers have slammed "blatant" attempts to manipulate the ballot, which will see the brother of a recently jailed three-time prime minister face off against a former World Cup-winning cricketer for leadership of the nuclear-armed nation, whose short history is peppered by coups and assassinations.

A series of deadly attacks in mid-July has further darkened the mood, denting optimism over hard-won security for the country of 207 million.