A candidate running for Pakistan's national assembly at historic polls next week was shot dead on Friday along with his three-year-old son in Karachi, police said.

It is the first time that a national assembly candidate has been killed in Pakistan's election campaign. Campaigning has been marred by Taliban threats and attacks, which have killed 62 people since April 11, according to an AFP tally.

Saddiq Zaman Khattak was a candidate for the Awami National Party (ANP), the leading secular party in Pakistan's ethnic Pastun northwest. A senior party leader said he had received threats.

"He was returning from a mosque after saying his Friday prayers with his three-year-old son when gunmen on a motorbike opened fire. Both were killed," police spokesman Imran Shaukat told AFP.

Senior ANP leader Bashir Jan confirmed the attack and the deaths.

There was no immediate claim of responsibility, but the Taliban has directly threatened ANP and the two other main parties in the outgoing government, branding the elections un-Islamic. (AFP)