Residents gather at the scene of a bomb explosion in Karachi.
Twin bomb explosions killed at least five people and injured 18 others in Pakistan's port city of Karachi on Friday, police said.
The two blasts took place within minutes of each other in the city's bustling, predominantly Shiite neighbourhood of Ancholi.
"The improvised explosive devices were planted on two motorbikes, which went off with a big bang, killing five people and injuring 18 others," senior local police official Javed Odho told AFP.
He said it was difficult to say immediately whether Shiites were the target because Sunnis also lived near the blast site.
Another senior local police official, Aamir Farooqi, confirmed the attacks and casualties.
The blasts, which damaged shops and cars, took place despite unusually tight security in the city, where at least 15,000 people attended a protest rally earlier in the day against sectarian violence in Rawalpindi last week that killed 11 people.
The demonstration was held in response to a countrywide call by Sunni sectarian organisation Ahle Sunnat Wal Jamaat.
Clashes erupted in Rawalpindi, which neighbours the capital Islamabad, last week when a procession by Shiite Muslims to mark the most important day of the mourning month of Muharram coincided with a sermon at a nearby Sunni mosque.
The groups attacked each other, TV cameramen and security forces, firing gunshots.
Karachi, a city of 18 million people, which contributes 42 percent of Pakistan's GDP, is rife with murder, kidnappings and has been plagued with sectarian, ethnic, and political violence for years.