Four people, including a senior Muslim cleric, were killed in a drive-by shooting in Pakistan's southern port city of Karachi, police said Friday.

Mufti Saeed Ahmed Jalalpuri, the senior leader of the Sunni Muslim group Jamaat ahl-e-Sunna, his son, and two associates died when four gunmen riding on two motorbikes opened fire at their vehicle late Thursday, officers said.

'Mufti died on the spot while three other people succumbed to their injuries later at the hospital,' said senior police officer Javed Meher, who said he suspected it could be a sectarian attack.

Tension gripped the city after the killings. Angry crowds fired shots in the air, forcing shops to close in some areas.

Thousands of people have been killed in sectarian violence between rival Sunni and Shiite extremist groups in recent years. They included two bombings that targeted a Shiite religious procession last month in Karachi, killing more than 30 people.