Pakistani police say two suspected suicide bombers were killed after their explosives detonated prematurely while riding a motorcycle in the volatile port city of Karachi.

Police say the men were travelling through a residential area of the city on Tuesday when the blast occurred, killing both men instantly.

Officials believe the men were carrying the explosives to an unknown location in Karachi to be used in a terrorist attack.

Hundreds of people have been killed in recent months in one of the worst waves of unrest in Karachi in years.

Many of the killings are blamed on ethnic gangs linked to rival political factions, such as the majority Urdu-speaking MQM and the mostly ethnic Pashtun Awami National Party.