At least 29 people were killed in different firing incidents in Pakistan's southern port city of Karachi on Thursday, taking death toll of the political and ethnic violence in the city to 65 in the last three days, reported local media.

According to the local media reports, at least 13 people were killed on Thursday afternoon when unknown gunmen fired at two buses in the city. Some 30 others were also injured in the attack.

Parts of Karachi had been tense the whole day on Thursday and most of petrol stations remained closed over security concerns. Long queues of cars and motorcycles were seen in front of open petrol stations in the city.

Government and private ambulance service had been busy to transfer the dead and injured to hospitals.

According to the local media reports, there had been grenade attacks on houses and shops, forcing the people to move to safe places.

Rival ethnic groups have blamed each other of target attacks, but local police said criminal gangs were also behind the fresh wave of violence in the city.

Residents in the city said that the police and paramilitary force have failed to check violence, but provincial police chief, Wajid Durrani, said the police are trying to lay heavy hands on miscreants.

The Muttahida Qaumi Movement, or MQM, a powerful ethnic group of Urdu-speaking people in the country, held an emergency meeting on Thursday to review the situation in the city. MQM will announce decisions of the meeting, but sources said it would give calls for strike if violence and "target killing" of its activists and supporters were not stopped.

The ethnic Pashtoon group "Awami National Party" (ANP) called for a military operation to clean the city from arms. The ANP leader Bashir Jan said that the police and the paramilitary force "Rangers" have failed to check violence and army can restore peace.