A powerful bomb exploded near a mosque in Pakistan’s largest city Karachi on Friday, killing at least four people and wounding 30 others, officials said.

A powerful bomb exploded near a mosque in Pakistan's largest city Karachi on Friday, killing at least four people and wounding 30 others, officials said.

The blast came outside a local mosque in the city's Delhi colony as worshippers were leaving after offering weekly Friday prayers.

A passing convoy of vehicles including a government car was initially thought to have been the target but provincial police chief Iqbal Mahmood said the theory had been discounted.

Mazhar Mishwani, the senior investigating officer of the Crime Investigation Department, told AFP that the bomb might have been planted to target a bus which routinely passes the road carrying minority Shiite Muslims.

Sagheer Ahmed, the health minister for Sindh province, told reporters that the blast killed four people and wounded 30 others, five seriously.

Mishwani said the 10-kilo bomb was planted under the back seat of an auto-rickshaw.

On Thursday, a senior policeman who had survived several assassination attempts was killed with three other people in a suicide attack in Karachi claimed by a Taliban faction.

The Pakistani government is in talks with the umbrella Tehreek-e-Taliban Pakistan (TTP) group to end their bloody seven-year insurgency, but the Mohmand chapter which claimed Thursday's attack has rejected the peace process.

Karachi, a city of 18 million people which contributes 42 percent of Pakistan's GDP, has been plagued for years by sectarian, ethnic and political violence.