One bomb exploded at a Sunni Muslim mosque in Malir district of Karachi, a congested middle-class neighborhood, killing four people and wounding at least 28 others, said police.
The bomb in the mosque exploded as worshippers knelt in the weekly Friday prayers.
The blast at the mosque came minutes after a bomb, hidden in a motorcycle, exploded outside a city court building in Karachi. It injured four people, two of them policemen, police said.
No one took responsibility for either explosion. The two blasts occurred in neighborhoods around 24 miles apart in the sprawling port city.
At the mosque, a witness who identified himself as Adnan Ahmed said he saw four men enter the mosque and leave behind a bag. Within minutes, he heard a loud explosion.
Residents of the area chased four people, capturing one of them. They handed him over to police, although it wasn't confirmed that he was involved in the bombing.
"I was in the back row when the bomb exploded. A piece of the roof fell on me and I passed out," said Haji Faiz Ahmed, whose hand was fractured by falling debris.
Many of the victims were Afghan nationals, who live and work in the area, said police.
The number of injured may increase, Karachi police commissioner Shafiq Pirachi said, because some of the wounded may have been taken to homes by relatives.
Azim Daoudpota, the governor of Sindh province, of which Karachi is the capital, blamed neighboring India for the explosion outside the court building. There was no immediate comment from New Delhi.
India and Pakistan, longtime rivals in South Asia, routinely accuse each other of carrying out acts of terrorism.
In recent weeks, several bombs have exploded in different cities in Pakistan killing and injuring dozens of people. In most cases Pakistan has blamed Indian agents.
By Zahid Hussain
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