Officials have said that a grenade attack in a mosque in Karachi, Pakistan, Wednesday night killed five people and raised the death toll in three days of violence to 76.

Police said the attack during evening prayers was perpetrated by at least two men who drove up to the mosque on a motorbike. One of them was seen going inside just before the blast, The English-language Pakistani newspaper Dawn has reported.

Adding the attackers then escaped, a police official said, "The Isha prayers were in progress when he hurled a hand grenade, which exploded in the middle of the third row."

According to Dawn, Karachi has been rocked by gunfire, arson and other violence since Syed Raza Haider, a senior leader of the Muttahida Qaumi Movement, was shot to death Monday. Beside those killed, scores more have been wounded.

Dawn further said that the city was rife with arson, as vehicles, shops and pushcarts were set ablaze in several neighborhoods.

The newspaper also added that the violence prompted many businesses to close and travel was limited.

Police claimed to have arrested 68 people suspected of being part of the rioting, said the state run Chinese news agency Xinhua. The news agency reported a higher number injured, more than 200.

Haider's party had declared three days of mourning to observe his death, Xinhua has said. (With Inputs from Agencies)