KARACHI (Reuters) - A gunman on a motorcycle shot dead three Pakistani Sunni Muslim leaders on Thursday, police said, in the latest apparent tit-for-tat killing in the southern financial hub of Karachi.

Conflict between Sunni and Shi'ite militants has been blamed for many recent killings in Pakistan's largest city.

At least 217 people have been killed this month, police sources say, but they do not know how many qualify as "target killings", the official term for assassinations.

"Three persons riding a bike intercepted (the victims')vehicle ... and one of them shot at persons sitting inside the car through the window pane," Deputy Inspector General of Police Abdul Aleem Jaffry said of the latest killings, which were caught on CCTV and broadcast on television.

He described them as target killings.

"We have no expectations of getting justice," said Qari Mohammad Usman, the Karachi chief of Jamiat-Ulema-e-Islam, one of the largest Sunni political parties.

"This entire nation, the citizens of Karachi, the students and clerics are exhausted from carrying the bodies of our elders ... The time is near when we will give a call for everyone to come out into the streets."

Interior Minister Rehman Malik told the Senate on Monday: "I want to alert the people of Pakistan to a possible disaster in Karachi as three groups have planned large-scale militancy."

(This story corrects name to Qari Mohammad Usman from Qari Mohammad Islam in paragraph 6)(Reporting by Imtiaz Shah in Karachi, Mubasher Bukhari in Islamabad and Reuters TV; Writing by Nick Macfie; Editing by Ruth Pitchford)